Dr. Riffat Asim Pasha
Transcript of Dr. Riffat Asim Pasha
FATIGUE BEHAVIOR OF PIEZOELECTRIC CERAMICS MATERIAL
Author Riffat Asim Pasha
03-UET/PhD-ME-03
Supervisor Dr. M. Zubair Khan
Department of Mechanical Engineering
Faculty of Mechanical & Aeronautical Engineering University of Engineering and Technology
Taxila, Pakistan 2009
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FATIGUE BEHAVIOR OF PIEZOELECTRIC CERAMICS MATERIAL
Author Riffat Asim Pasha
03-UET/PhD-ME-03
A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (PhD) in Mechanical Engineering.
Checked and Recommended by:
a. The Research Committee:
Dr. M. Zubair Khan Research Supervisor
Dr. M. Asif Khan Dr Muhammad Shuaib Dr Zafarullah Koreshi Member Member Member
b. Foreign Experts i. Dr A.N.K Jadoon ii. Prof.Dr Muhammad Sarwar
U.K U.K Approved By
Dr M. Zubair Kkan Supervisor
External Examiner External Examiner Dr Zafar M. Khan Prof. Dr Arshad Hussain Qureshi
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ACKNOWLEDGEMENTS
Alhamdulillah-ha- Rabal Aalamin, who gives me knowledge, wisdom and courage to
complete this research work. May Allah make this work useful for me and for others in
future (Aamin).
After this I would like to say special thanks to my supervisor Dr M. Zubair Khan who
provide me the knowledge and guidance, motivated me in crucial periods and encourage
me at each and every moment during this research work. His continuous involvement and
invaluable suggestions are remarkable.
My special thanks and gratitude is for Prof. Dr Tahir I Khan (Mechanical and
Manufacturing Engineering Department, University of Calgary, Canada). In fact I was
able to do the experimental work due to his kind invitation and supervision of my work
during my stay in Canada. He is really a source of inspiration for me which I can never
forget. I am also thankful to my research committee members, Dr. M.Asif Khan, Dr
Muhammad Shuaib, and Dr Zafrullah Koreshi, who provided me continuous guidance
and invaluable suggestions during my research work.
I am thankful to Dr A.N.K Jadoon and Prof. Dr Muhammad Sarwar for their invaluable
suggestions and evaluation of my thesis. I have best regards for Prof. M. Anwar Khan,
and Prof. Dr Mukhtar Hussain. Sahir, they always motivated me to complete this work. I
am really thankful to Prof. Dr Shahab Khushnood, for his continuous encouragement and
kept me relaxed from the additional academic and administrative load during my research
period. I am grateful to Prof. Dr. M.M.I Hammouda for his invaluable guidance and extra
ordinary help and motivations.
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I am thankful to Dr Zafar M Khan and Prof. Dr Arshad Hussain Qureshi for conducting
the defense and oral examination and given valuable suggestions to incorporate in my
thesis.
I must thank to Higher Education Commission, Pakistan for funding to visit University of
Calgary, Canada as visiting research fellow for six months. I must appreciate the great
help by Dr Keler (Electrical Engineering Department, University of Calgary) who
provide the facility to take electrical measurement in his laboratory. I can not forget the
invaluable assistance of Mr Jim Mcneely (Calgary University), who fully cooperated in
technical assistance during all my experimentation. I appreciate assistance of Mr. Abdul
Aziz (Calgary University) in research laboratory. I am thankful to Dr Azfar Hassan
(Chemical Engg. Deptt.(Calgary University) for his cooperation.
I must thankful to Director Research Prof. Dr Qaiser-uz Zaman and his staff members Mr
Zafar Iqbal and Mr Zaheer Shah for their continuous support in fulfilling the
documentation and funding requirements. I must remember my friends Dr Jahanzaib
Mirza, Zahid Suleman Butt and Dr. Gulistan Raja for their continuous moral support and
assistance in editing. I am also thankful to Mr Khalid Mehmood, Mr Zahid Iqbal, Irfan
Ali, Muhammad Irfan and Jam Muhammad Nadeem Ahsan for their support and
assistance.
At the end I express me deepest gratitude to my mother who always pray for my success
and my other family members. I must thank to my wife for her patience during my
research commitments, specially during my stay abroad she managed the home very well
and definitely my kids Ramla and Sharjeel, those suffered a lot and scarified their time
during my whole research period.
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DECLARATION
It is certified that PhD research work titled “Fatigue Behavior of Piezoelectric
Ceramics Material” is my own work. The work has not been presented elsewhere for
assessment. The material used from any other source has been properly acknowledged.
Author
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ABSTRACT Piezoelectric ceramics materials are extensively used in many electromechanical systems
as sensing and actuating devices. The performance of these devices deteriorates due to
cyclic loading either mechanical, electrical, electromechanical, thermo-mechanical, and
under thermal shocking conditions. Earlier the effect of electrical and mechanical cycling
loadings on the functional performance has been investigated. The properties of
commercial lead zirconate titanate degrade during such cycling. However degradation
phenomenon of piezoelectric material during thermal shocking is still an area which has
to be explored. The decay in functional properties of materials is somewhat called
degradation and this terminology used to describe the loss in performance with time due
to stress and temperature. The common phenomenon of degradation is aging of the
material, which affects the performance of the material with time. This change in
performance is thought to be due to re-orientation of dipoles in different configurations.
Environment is another degradation phenomenon influence the performance of piezo
devices. Output performance of piezoelectric materials changes frequently with the
change in temperature, pressure, humidity and moisture. Recently many studies show that
water has the profound effect on the performance of piezoelectric materials. Reliability of
these smart materials is important and hence there is a requirement to have an extensive
study on its functional performance and properties. In actuators mostly disc shaped
piezoelectric are used due to their improved properties. A part of this particular research
work was to investigate the degradation of thin lead zirconate titanate piezoelectric discs
through a series of experimentation to observe its function at variable frequencies in
simple tap water, de-ionized water and sodium chloride (NaCl) solutions. Output
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performance has been monitored in real time as peak-peak voltage change. PZT disc
found sensitive in performance in various solutions at different frequencies. The results
obtained can be utilized as qualitative data for designing of micro electro- mechanical
systems.
The change in capacitance has been measured by using relevant instrumentation during
thermal shocking in de- ionized water. The change in capacitance is a measure of
dielectric constant and other piezoelectric properties. Dielectric constant, impedance,
tangent loss and dissipation factors are the required parameters and can be measured by
using suitable size and shape of piezoelectric materials. In general, piezoelectric ceramics
posses the largest electromechanical coupling factor, dielectric constant and lowest
dielectric loss. The sudden change in temperature may experience a thermal stress which
further changes its above stated properties. Most of the properties are attributed to change
in capacitance values at resonance and anti resonance frequencies. In a part of this
research work, focus was to determine the various piezoelectric properties by thermal
shocking in de-ionized water at resonance frequencies.
In another phase piezoelectric ceramics disc has been investigated for its sensitivity at
different temperatures and at different frequencies and resistances. A model has been
developed to indicate the effect of resistance band at different temperatures. The model of
performance characteristics of thin PZT disc under different temperature conditions is a
unique finding and may used in selection of particular frequency and resistance range for
many piezo devices for the stated conditions.
The objective of this research work was to explore the degradation of thin PZT
piezoelectric ceramics disc in its performance and change of various piezoelectric
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properties during thermal cycling and shocking. The present work uncovers the various
unattended thermal cycling and shocking condition of stated piezoelectric material.
Comprehensive data obtained by real time experimentation may useful for designing of
various micro-electromechanical systems.
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TABLE OF CONTENTS
CHAPTER Description Page
Title page i
Title page with signatures ii
Acknowledgements …..iii
Declaration ……v
Abstract vi
Table of contents .ix
List of Figures xiv
List of Tables xviii
1 Introduction
1.1 Introduction………………………………………………………………01
1.2 Research Theme……………………..……………………………...........01
1.3 Aims and Objectives of Research………………………..………………02
1.4 Thesis Organization………………………………………………...........04
2 Literature Review
2.1 Introduction………………………………………………………………05
2.2 Piezoelectricity……………………………………………………...........05
2.3 Polarization….……………………………………………………...........07
2.4 Mathematical Description of Piezoelectric Effect ………………...........08
2.5 Historical Background…………………………………………………...11
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2.6 General Characteristic, Fabrication and Processing of PZT……………...13
2.7 Piezoelectric Crystal Classes………………………………………….....19
2.7.1 Lead Zirconate Titanate (PZT)………………………………......20
2.7.2 Barium Titanate……………………………………………….....21
2.7.3 Polyvinylidene Fluoride (PVDF)……………………………...…22
2.8 Recent Development in Piezoelectric Ceramics………………………....22
2.9 Thermal Cycling and Shocking in Piezoelectric…………………………25
2.10 Effect of Water and Moistures in Piezoelectric Ceramics……………….29
3 Experimental Methodologies
3.1 Introduction…………………………………………………..………..…31
3.2 Standard Fatigue Testing Methodologies……………..………………....31
3.3 Thermal Cyclic Loading in Piezoelectric Ceramics……………………..32
3.4 Selection of Specimen………………………………………….………..33
3.5 Resonance Method………………………………………………………34
3.5.1 Measurement of Material Properties………………………..…..35
3.5.2 Density Calculation……………………………………….….....39
3.5.3 Calculation of Free Relative Dielectric Constant………….……39
3.5.4 Calculation of Coupling……………………………..……….....39
3.6 Determination of Elastic, Piezoelectric, and Dielectric Constant …..….40
3.7 Selection of Experimental Setup/Design of Experiments………….......40
3.7.1 Phase-1 Performance of PZT and Its Effect Due to Water…….41
3.7.2 Phase-2 Thermal Cycling/Shocking Effect of Thin PZT Disc....41
3.7.3 Phase-3 Thermal Cycling Effect…………………………….....42
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3.8 Research Contribution…………………………………………….…....42
3.8.1 Phase-1……………………………………………………........42
3.8.2 Phase-2……………………………………………………........42
3.8.3 Phase-3……………………………………………………........43
3.9 Measurements……………………………………………………….…43
3.10 Capacitance Measurement by 6451B Dielectric Test Fixture…………44
3.10.1 Specifications……………………………………………….....44
3.10.2 Performance Characteristics……………………………....…..45
3.10.3 Selection of Electrodes…………………………………..…....45
3.10.4 Operation………………………………………………………46
3.10.5 Contacting Electrode Method………………………………….46
3.10.6 Testing Material……………………………………………….46
3.10.7 Error Correction……………………………………………….47
3.10.8 Electrode Adjustment…………………………………………47
3.10.9 Measurement Procedure………………………………………47
3.11 Designed Circuitry for Frequency Determination……………………48
3.11.1 Switch Box Circuit……………………………………….…..49
3.11.2 Oscillator Circuit……………………………………..…........52
3.11.3 Frequency Counter…………………………………………...53
3.11.4 Decade Resistor Circuit……………………………………....53
3.11.5 Wave Form Generator………………………………..……....55
3.11.6 Voltmeter………………………………………………..........55
3.11.7 Frequency Measuring Procedure………………………..........55
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3.12 Measurement and Effect of Thickness by ANSYS……………………..57
4 Experimentation and Analysis of Results
4.1 Introduction………………………………………..……………58
4.2 Phase-1………………………………………………………....58
4.2.1 Piezoelectric Material…………………………..……...............61
4.2.2 Test Setup and Variables………………………….……….…..62
4.2.3 Results and Discussion……………………………….……..…64
4.3 Phase-2 (Series 1)……………………………………………...82
4.3.1 Specimen………………………………………………………82
4.3.2 Instrumentation……………………………………………......82
4.3.3 Testing /Measurements………………………………………..82
4.4 Thermal Shocking from 1000C from Thermal Chamber to De-Ionize
Water at 200C………………………………………………..…………..…...83
4.4.1 Test Setup &Variables……………………………………….85
4.4.2 Results Analysis…………………………..………………….88
4.5 Phase-2 (series 2)……………………………………………............95
4.5.1 Experimentation…………………………………………..…95
4.5.2 Results Analysis……………………………………………..97
4.6 Phase-3 (series 3)…………………………………………….……..101
4.6.1 Experimental Setup………………………………....102
4.6.2 Experimentation………………………………….…105
4.6.3 Series-1 (at room temperature, 200C)………………106
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4.6.4 Series-2 (at 160 0C)……………………………..........111
4.6.5 Development of a Model……………………..….…..118
4.7 Discussions…………………………………………………………..126
4.7.1 Effect of Water on PZT Disc………………………………….…...….126
4.7.2. Thermal Cycling/Shocking of Thin PZT Disc [From 100 0C (Thermal
chamber ) to 20 0C (In de-ionized water)]……………………………..........127
4.7.3 Thermal Cycling/Shocking of Thin PZT Disc From 100 0C &150 0C
(Thermal chamber) to20 0C (In de-ionized water)……………………….....130
4.7.4 Effect of Frequency and Resistance on peak-peak voltage in two different
Thermal Conditions………………………………………………………….131
5 Conclusions and Future Recommendations
5.1 Conclusions 132
5.2 Future Recommendations 134
References………………………………………………………………….… 137
APPENDIX-A: Thermal cycling/shocking results images of thin PZT disc APPENDIX-B: List of Pertinent PhD Publications.
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LIST OF FIGURES
Fig.2.1 Phase Stability in the System Pb(Ti1-x Zrx)O3 ...................................................... 14
Fig.2.2 Coupling Coefficient kp and Permittivity εr Values Across the PZT Compositional
Range ...................................................................................................................................... 15
Fig.3.1 Experimental circuit for the determination of fm and fn ......................................... 49
Fig. 3.2 Switch Box Circuit................................................................................................... 50
Fig. 3.3 Oscillator circuit ....................................................................................................... 52
Fig. 3.4 Decade resistor circuit ....................................................................................... 54
Fig. 3.5 Waveform Generator ....................................................................................... 54
Fig. 4.1 Schematic Arrangement for the determination of Pk-Pk Voltage at variable
frequencies ............................................................................................................................. 62
Fig. 4.2 Variation of peak to peak voltage as a function of frequency. ............................. 63
Fig. 4.3 Heating time as a function of peak to peak voltage in ordinary water. ............... 76
Fig. 4.4 The change in voltage as a function of drying time after immersion in ordinary
water……………………………………………………………………………………...76
Fig. 4.5 Heating time as a function of peak to peak voltage in de-ionized water. ............. 77
Fig. 4.6 The change in voltage as a function of drying time after immersion in de-ionized
water. ...................................................................................................................................... 77
Fig.4.7 Heating time as a function of peak to peak voltage in NaCl
solution…………………………………………………………………………………..78
Fig. 4.8 The change in voltage as a function of drying time after immersion in NaCl
solution. .................................................................................................................................. 78
Fig. 4.9 Rate of change in temperature and shocking ......................................................... 85
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Fig. 4.10 Impedance analyzer connected with test fixture for measuring various
parameters (Impedance, Capacitance, Dissipation factor, Phase angle). ........................... 88
Fig. 4.11 Value of capacitance for Un-shocked Disc ……………………………………90
(a). Capacitance at frequency of maximum impedance
(b). Capacitance at frequency of minimum impedance
Fig. 4.12 Value of capacitance after thirty five shocks……………………..……………91
(a). Capacitance at frequency of maximum impedance
(b). Capacitance at frequency of minimum impedance
Fig. 4.13 Change in Dielectric constant against Number of shocks…………………..…92
Fig. 4.14 Coupling Factors against Number of Shocks ....................................................... 92
Fig. 4.15 Change in dielectric constant against number of shocks, at frequency 1KHz, at
frequency of maximum impedance, at frequency of minimum impedance. ..................... 98
Fig. 4.16 Change in coupling factor (K31, Keff) against number of shocks from 1000C –
200C & from 1500C – 200C in de-ionized water.. ............................................................... 99
Fig. 4.17 Change in Modulus of impedance ( |Z| ) against number of shocks from 1000C –
200C & from 1500C – 200C in de-ionized water.. ............................................................... 99
Fig. 4.18 Experimental arrangement for the determination of out put voltage ................ 103
Fig. 4.19 Schematic arrangement of thermal cycling circuitry .......................................... 104
Fig. 4.20 Soldered Piezoelectric PZT disc (diameter 12.7mm and thickness 0.191mm) .. 106
Fig. 4.21 Experimental arrangement for the determination of output voltage at room
temperature (200C) . ............................................................................................................ 107
Fig. 4.22 Effect of resistance on Pk-Pk voltage at various frequencies at 200C………..108
Fig. 4.23 Change in Pk-Pk voltage for each 100kΩband at 200C……………………...110
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Fig. 4.24 Effect of resistance at Pk-Pk voltage at various frequencies and at 1600C ...... 113
Fig. 4.25 Change in Pk-Pk voltage for each 100kΩ band at 1600C…………………….114
Fig. 4.26 Effect of temperature on Pk-Pk Voltage at frequency 50 Hz against change in
Resistance……………………………………………………………………………....115
Figure 4.27 Effect of temperature on Pk-Pk Voltage at frequency 100 Hz against change
in Resistance……………………………………………………………………………115
Figure 4.28 Effect of temperature on Pk-Pk Voltage at frequency 150 Hz against change
in Resistance……………………………………………………………………………116
Figure 4.29 Effect of temperature on Pk-Pk Voltage at frequency 200 Hz against change
in Resistance………………………………………………………………………..…..116
Figure 4.30 Effect of temperature on Pk-Pk Voltage at frequency 300 Hz against change
in Resistance………………………………... ………………………………………...117
Figure. 4.31 Difference in Pk-Pk value against Resistance band number at 50Hz……119
Figure. 4.32 Difference in Pk-Pk value against Resistance band number at 100Hz…..120
Figure. 4.33 Difference in Pk-Pk value against Resistance band number at 150Hz…..120
Figure. 4.34 Difference in Pk-Pk value against Resistance band number at 200Hz…..121
Figure. 4.35 Difference in Pk-Pk value against Resistance band number at 300Hz…..121
Figure. 4.36 Exponential coefficient A against Frequency in Hz at 200C…………….122
Figure 4.37 Exponential coefficient B against Frequency in Hz at 200C……………..122
Figure. 4.38 Difference in Pk-Pk value against Resistance band number at 50Hz……123
Figure. 4.39 Difference in Pk-Pk value against Resistance band number at 100Hz…..123
Figure. 4.40 Difference in Pk-Pk value against Resistance band number at150Hz……124
Figure. 4.41 Difference in Pk-Pk value against Resistance band number at 200Hz…...124
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Figure.4.42 Difference in Pk-Pk value against Resistance band number at 300Hz……124
Figure-4.43 Exponential coefficient A against Frequency in Hz at 200C……………...125
Figure-4.44 Exponential coefficient A against Frequency in Hz at 200C ……………..125
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LIST OF TABLES
Table 3.1: Description of Specimen (PSI-5A4E Single Layer Disks) ............................... 33
Table 3.2 Parent Specimen Properties as provided by supplier (PIEZO SYSTEM INC. USA)…..34
Table 3.3 Description of various electrodes and their selection…………………………45
Table3.4 Selection of Resistance in Switch-2……………………………………...……51
Table3.5 Selection of Resistance for Switch I & Switch II………………………… …54 Table 4.1 Heating time in ordinary water and respective voltage at 50Hz ........................ 65
Table 4.2 Heating time in ordinary water and respective voltage at 100Hz ...................... 65
Table 4.3 Heating time in ordinary water and respective voltage at 150Hz……………..66 Table 4.4 Heating time in ordinary water and respective voltage at 200Hz…… ………66
Table 4.5 Drying Time after taking out from ordinary water at 50Hz…………………...66
Table 4.6 Drying Time after taking out from ordinary water at 100Hz ............................. 67
Table 4.7 Drying Time after taking out from ordinary water at 150Hz ............................. 67
Table 4.8 Drying Time after taking out from ordinary water at 200Hz…………………67 Table 4.9 Heating Time in De-ionized water and respective voltage at 50Hz………….68 Table 4.10 Heating Time in De-ionized water and respective voltage at 100Hz .............. 68
Table 4.11 Heating Time in De-ionized water and respective voltage at 150Hz………..68
Table 4.12 Heating Time in De-ionized water and respective voltage at 200Hz………..69
Table 4.13 Drying time after taking out from de-ionized water at various frequencies…69
Table 4.14 Heating Time in NaCl solution and respective voltage at 50&100Hz…...….70
Table 4.15 Heating Time in NaCl solution and respective voltage at 150&200Hz…….70
Table 4.16 Drying Time after taking out from NaCl solution at 50 & 100Hz…………..71
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Table 4.17 Drying Time after taking out from NaCl solution at 150 & 200Hz……..…73
Table-4.18 Values of Capacitance, Coupling factors ,and dielectric constant at frequency
of maximum (fm) and frequency of minimum (fn) impedance………………………....87
Table-4.19 Change in Dielectric Constant and Coupling Factor for two Different Thermal
Shocking Conditions…………………………………………………………………...97
Table-4.20 Change in Pk-Pk Voltage against Resistances at 200C (RT)*………….…107
Table 4.21 Difference in voltage for each 100kΩ band at 200C………………………109
Table 4.22 Resistance Range Bands………………………………………………..…110
Table-4.23 Change in Pk-Pk Voltage against Resistances at 1600C………………….112
Table-4.24: Difference in voltage for each 100kΩ band at 1600C…………………....113
1
CHAPTER # 1
INTRODIUCTION
1.1 Introduction
There has been a growing interest in recent years in piezoelectric ceramics
materials due to their numerous applications. These material exhibits very interesting
behavior for which they are being used extensively in various micro electromechanical
systems as sensing and actuating devices. Micro-electromechanical systems (MEMS) are
playing an important role in the field of electronics and mechatronics. Recently these
systems are manufactured by using natural and synthetic fabricated ceramic crystals. The
structures in which these materials are used are normally under the influence of various
cyclic loads. These cyclic loads may be mechanical, electrical, electromechanical, and
thermal [1]. Most of the piezoelectric ceramic materials are polycrystalline ceramics
instead of natural piezoelectric crystals. These are more versatile with physical, chemical
and piezoelectric characteristics. PZT ceramics can be manufactured to almost any given
shape or size. They are chemically inert, and immune to moisture and other atmospheric
conditions. There are still various conditions in which the behavior of these materials
needs the attention of present researchers.
.
1.2 Research Theme
Piezoelectric materials used in different sensing and actuating devices may
degrades in its properties. These properties may affect the performance and functioning
in their operation. Degradation in their properties due to mechanical and electrical fatigue
2
has been extensively studied and there was a research gap in finding the characteristics of
these materials in thermal cycling and particularly in thermal shocking and quenching.
Lead zirconate titanate (PZT) based ceramics are widely used for their excellent
piezoelectric properties and these properties may degrade due to the application of
mechanical, electrical, electromechanical, and thermal loadings. Lot of work is being
carried out in exploring the fatigue behavior of these smart materials when subjected to
electrical and electromechanical loading conditions. Fatigue studies have shown that the
degradation in material properties is strongly influenced by temperature. Temperature
plays an important role in dictating the electromechanical response of piezoelectric
materials. In this research work, thin PZT discs have been investigated for their cyclic
and shocking behavior in thermal loading conditions. The purpose was to test the PZT
under various thermal environments and examine the degradation in their properties. The
degradation in materials properties affects the functional performance characteristics of
the instrument in which these smart materials are being used.
1.3 Aims and Objectives of Research
The present work aimed to investigate the change in functional performance and internal
characteristics of lead zirconate titanate thin disc during thermal cycling of thin PZT disc
in different conditions. The work has been divided in three major phases of
experimentation. Phase-1 is to determine the change in output potential during thermal
cycling in three different water conditions. Performance of PZT material affected by
environmental factor has been reported. In phase-2 the change in piezoelectric properties
with the change in capacitance and dielectric constant at resonance and anti–resonance
3
frequencies has been examined during thermal shocking in de-ionized water. The results
are the basis for the determination of other piezoelectric properties.
Effect of frequencies and resistances on output potentials at variable temperatures have
been analyzed real time in phase-3. Comprehensive quality data has been obtained which
may used for the designing of smart piezoelectric devices.
By considering the tested and analyzed data, following objectives have been
achieved in this research work.
• To understand the nature and behavior of selected PZT disc during thermal
cycling in different water conditions. (In simple tap water, in de-ionized water and
in NaCl solution).
• To find the change in dielectric constant, capacitance and other piezoelectric
properties by obtaining the quality data at resonance and anti resonance
frequency.
• How thermal shocking in de-ionized water affects the piezoelectric properties of
the selected grade and size of PZT material.
• The effect of thermal shocking temperature difference on its piezoelectric
properties has been investigating through sensitivity analysis.
• Development of a model elaborates the performance characteristics at variable
frequency and resistance bands (0kΩ to 1000kΩ) at two different specific
temperatures.(200C and 1600C)
4
1.4 Thesis Organization
Thesis has been organized as follow:
This chapter is a brief introduction of scope and objectives of this particular research
work. The descriptions of piezoelectricity and mathematical description of piezoelectric
material along with comprehensive literature review has been presented in chapter-2.
This chapter also includes the brief history, applications and the descriptions of the
previous work relating fatigue behavior of piezoelectric ceramics under various loading
conditions. Existing and proposed research methodology, experimental arrangements,
and circuitry design to measure the frequency of maximum and minimum impedance at
various frequencies have been described in chapter 3. All three experimental phases have
been elaborated in chapter 4. In phase-1, effect of water on performance characteristics of
piezoelectric ceramic discs in different mediums has been described. Thermal cycling and
shocking effects have been determined in phase-2. Thermal cycling using variable
frequencies and resistances and at different temperatures has been analyzed in phase-3 of
the same chapter. Results analysis and a mathematical model to describe the behavior of
the material in different conditions have been described in the same chapter. The
elaborated analysis and discussions on results have also been described in the same
chapter. Conclusions and future recommendations are presented in Chapter 5.
Last but not least the current research work is to explore the unattended behaviors of thin
PZT disc in thermal cycling/shocking environment at variable conditions.
5
CHAPTER# 2
LITERATURE REVIEW
2.1 Introduction
Piezoelectric ceramics materials play an important role in the field of smart
structures. The degradation in their internal characteristics affects their efficiency and
performance. This chapter reviews a brief historical background. Piezoelectric crystal
classes, their characteristics. Fabrication and processing techniques have also been
described. A comprehensive review on the degradation behavior of piezoelectric ceramic
subjected to thermal cycling and shocking condition is presented.
2.2 Piezoelectricity
The phenomenon of piezoelectricity was discovered in the late nineteenth century. It was
observed that certain materials generate an electric charge or voltage when they are under
mechanical stress. Alternately, these materials produce a mechanical stress when they are
subjected to an applied voltage [2].
In 1880, Pierre and Jacques Curie experimentally discovered the direct piezoelectric
effect in various naturally occurring substances. In 1881, Hermann Hankel suggested
using the term piezoelectricity, which is derived from the Greek “piezen” meaning “to
press.” In 1893, Willam Thomson published seminal papers on the theory of
piezoelectricity. It was mathematically hypothesized and then experimentally proven that
a material exhibiting both, the generation and actuation effect.
6
Piezoelectricity is a property of certain classes of crystalline materials including natural
crystals and manufactured ceramics such as barium titanate and lead zirconate titanate
(PZT). The piezoelectricity phenomenon was developed and applied in sonar and quartz
oscillation crystals. In 1921, Walter Cady invented the quartz crystal-controlled oscillator
and the narrow band quartz crystal filter used in communication systems. Two important
artificial piezoelectric crystals, barium titanate, and lead zirconate titanate were invented
in the early 1950s [3]. The surface charge leads to mechanical strain either compressive
or tensile depends upon the direction of applied polarity of the applied voltage. The
phenomena occur only in those crystals having no centre of symmetry. As piezoelectric
materials have excellent capability to convert an electrical signal to mechanical and
mechanical to electrical and therefore have high electromechanical coupling factor. A
especially cut electroded piezo crystal detect the longitudinal transverse vibration in
solid. These mechanical vibrations converted to electrical signal and can be displayed on
oscilloscope. One of the most important applications of the piezoelectric material is in the
frequency control of oscillator and filters whenever a mechanical force is setup in these
materials they vibrate at certain frequency. The frequency of these mechanical vibrations
has certain wavelength. These mechanical vibrations have very small losses and therefore
have a high quality factor Q. With the excitation of PZT materials, Impedance at
maximum and minimum frequency is the measure of coupling factor. Higher is the
difference between these two referenced frequencies, higher is the coupling factor
between fm and fn the response of the transducer is controlled by the mass of the material
[4]. Piezoelectric materials are being used in MEMS sensors and actuators. Think-film
piezoelectric materials have been explored for use as on-chip acoustic transducers,
7
pumps, accelerometers, and microphones and mainly as actuators and sensors in the
aerospace and marine industries [2]. The effect also useful application for the production
and detection of sound, generation of high voltages, electronic frequency generation,
microbalance, and ultra fine focusing of optical assemblies [5].
2.3 Polarization
Many important properties of piezoelectric materials stem from their crystalline
structures. Piezoelectric crystals can be considered to be a mass of minute crystallites
(domains). The macroscopic behavior of the crystal differs from that of individual
crystallites, due to the orientation of such crystallites. The direction of polarization
between neighboring crystal domains can differ by 900 or 1800. Owing to the random
distribution of domains throughout the material, no overall polarization or piezoelectric
effect is exhibited. A crystal can be made piezoelectric in any chosen direction by poling,
which involves exposing it to a strong electric field at an elevated temperature. Under the
action of this field, domains most nearly aligned with the field will grow at the expense
of others. The material will also lengthen in the direction of the field, when the field is
removed, the dipoles remain locked in an approximate alignment, and crystal becomes
polarized.
The poling treatment is usually the final step of crystal manufacturing. Care must be
taken in all subsequent handling and use to ensure that the crystal is not depolarized,
since this will result in a partial or even total loss of its piezoelectric effect.
For static fields, the threshold is typically between 200-500 V/mm.
Mechanical depolarization occurs when mechanical stress on a piezoelectric element
becomes high enough to disturb the orientation of the domains and hence destroy the
8
alignment of the dipoles. If a piezoelectric element is heated to a certain threshold
temperature, the crystal vibration may be so strong that domains become disordered and
the element becomes completely depolarized. This critical temperature is called the Curie
point or the Curie temperature. A safe operating temperature would normally be halfway
between 00C and the Curie point. The properties of piezoelectric elements are time
dependent and the stability of a piezoelectric as a function of time is of particular interest
[2]. Piezoelectric materials are crystals. The microscopic origin of piezoelectricity is the
displacement of ionic charges with a crystal, leading to the polarization and electric field.
A stress (tensile or compressive) applied to a piezoelectric crystal will alter the spacing
between centers of positive and negative charge sites in each domain cell; this leads to a
net polarization manifested as open circuit voltages measurable at the crystal surface.
Compressive and tensile stresses will generate electric fields which will exert a force
between the centers of positive and negative charges, leading to an elastic strain and
changes of dimensions depending on the field polarity. The direction of the induced
polarization depend on the direction of applied stress generally the applied stress in one
direction can give rise to induced polarization in other direction and reversing of stress
reverse the polarization direction [4]
2.4 Mathematical Description of Piezoelectric Effect
In a piezoelectric crystal, the constitutive equation that relates electrical polarization (D)
and applied mechanical stress (T) is
D= dT + εE (1.1)
9
Where d is the piezoelectric coefficient matrix, ε the electric permittivity matrix, and E
the electrical field. The electrical polarization is contributed by two parts-one stemming
from electrical biasing and one from mechanical loading.
If no electric field is present (i.e.., E=0), then the second term on the right-hand side of
Equation (1.1) can be eliminated.
The General Constitutive Equation can be written in the full matrix form:
T1 D1 d11 d12 d13 d14 d15 d16 T2 ε11 ε12 ε13 E1 D2 = d21 d22 d23 d24 d25 d26 T3 + ε21 ε22 ε23 E2 D3 d31 d32 d33 d34 d35 d36 T4 ε31 ε32 ε33 E3 T5
T6
The terms T1 through T3 are normal stress along axes 1, 2, and 3, whereas T4 through T6
are shear stresses. The units of electrical displacement (Di) stress (Tj), permittivity (εi),
and electrical field (Ej) are C/m2, N/m2, F/m, and V/m, respectively. The unit of the
piezoelectric constant dij is the unit of electric displacement divided by the unit of the
stress namely.
[ ] [ ][ ]
[ ] [ ][ ] N
Columb
mNmm
TEVF
TDdij ====
2
ε (1.3)
(1.2)
10
Equation 1.4 can be expanded to a full matrix from:
(1.5)
(1.6)
The inverse effect of piezoelectricity can be similarly described by a matrix-form
constitutive equation. In this case, the total strain is related to both the applied electric
field and any mechanical stress, according to
S = ST + dE, (1.4)
Where s is the strain vector and S is the compliance matrix.
If there is no mechanical stress present (Ti,i=1,6=0), the strain is
related to the electric field by
Note that, for any given piezoelectric material, the dij components connecting the strain
and the applied field in the inverse effect are identical to the dij connecting the
polarization and the stress in the direct effect [2]. The unit of dij can be confirmed from
Equation (1.6) as well. It is (m/m)/(V/m = m/V = C/N.
11
The electromechanical coupling coefficient k is a measure of how much energy is
transferred from electrical to mechanical energy, or vice versa, during the actuation
process and is calculated as defined [6].
EnergyConverted
InputEnergyK =2 (1.7)
This relation holds true for both mechanical-to-electrical and electrical-to-mechanical
energy conversion. The magnitude of k is a function of not only the materials, but also the
geometries of the sample and its oscillation mode [2]
2.5 Historical Background
The piezoelectric effect dates back to thousands of years was first noticed in rocks
which would repel other rocks when they were heated. These rocks, which were actually
Tourmaline crystals, eventually found their way into Europe. Once the crystals arrived in
Europe, they were scrutinized by the scientists. In the mid 1700’s, this effect was given
the name of pyroelectricity, which means electricity by heat. Pyroelectricity is the ability
of certain mineral crystals to generate electrical charge when heated, was known as early
as the 19th century, and was named by David Brewster in 1824. In 1880, the brothers
Pierre Curie and Jacques Curie predicted and demonstrated piezoelectricity using tinfoil,
glue, wire, magnets, and a jeweler's saw. They showed that crystals of tourmaline, quartz,
topaz, cane sugar, and Rochelle salt generate electrical polarization from mechanical
stress. Quartz and Rochelle salt exhibited the most piezoelectricity effects. The second
practical application for piezoelectric devices was sonar, first developed during World
War I. In France in 1917, Paul Langevin (whose development now bears his name) and
his fellows developed an ultrasonic submarine detector. The detector consisted of a
12
transducer, made of thin quartz crystals carefully glued between two steel plates, and a
hydrophone to detect the returned echo. By emitting a high-frequency chip from the
transducer, and measuring the amount of time it takes to hear an echo from the sound
waves bouncing off an object, one can calculate the distance to that object. The use of
piezoelectricity in sonar, create an interest in piezoelectric devices. Over the next few
decades, new piezoelectric materials and new applications for those materials were
explored and developed. Development of piezoelectric devices and materials in the
United States was kept within the companies involved in the development, mostly due to
the wartime beginnings of the field, and in the interests of securing profitable patents.
Quartz crystals were the first commercially exploited piezoelectric material, but scientists
searched for higher-performance materials. Piezoelectric devices found homes in many
fields. Ceramic phonograph cartridges simplified player design, were cheap and accurate,
and made record players cheaper to maintain and easier to build. Ceramic electric
microphones could be made small and sensitive. The development of the ultrasonic
transducer allowed for easy measurement of viscosity and elasticity in fluids and solids,
resulting in huge advances in materials research. Ultrasonic time-domain reflecto-meters
(which send an ultrasonic pulse through a material and measure reflections from
discontinuities) could find flaws inside cast metal and stone objects, improving structural
safety. However, despite the advances in materials and the maturation of manufacturing
processes, the United States market had not grown as quickly. Without many new
applications, the growth of the United States' piezoelectric industry suffered. In contrast,
Japanese manufacturers shared their information, quickly overcoming technical and
manufacturing challenges and creating new markets. Japanese efforts in materials
13
research created piezoceramic materials competitive to the U.S. materials, but free of
expensive patent restrictions. Major Japanese piezoelectric developments include new
designs of piezoceramic filters, used in radios and televisions, piezo-buzzers and audio
transducers that could be connected directly into electronic circuits, and the piezoelectric
igniter which generates sparks for small engine ignition systems (and gas-grill lighters)
by compressing a ceramic disc. Ultrasonic transducers that could transmit sound waves
through air had existed for quite some time, but first saw major commercial use in early
television remote controls. These transducers now are mounted on several car models as
an echo location device, helping the driver determine the distance from the rear of the car
to any objects that may be in its path. Historically, well known applications of
piezoelectric sensors have included phonograph pickups, microphones, acoustic modems,
and acoustic imaging for underwater, underground objects and medical instrumentation
[7]. The first ceramic to be developed commercially was BaTiO3. By the 1950s the solid
solution system Pb (Ti, Zr)O3 (PZT), which also the perovskite structure, was found to be
ferroelectric and PZT compositions are now the most widely exploited of all piezoelectric
ceramics [8].
2.6 General Characteristics, Fabrication and Processing of PZT
The Pb (Zr1-x Tix)O3 phase diagram is shown in figure 2.1. The morphotropic
phase boundary (MPB) defines the composition at which there is an abrupt structural
change, the composition being almost independent of temperature. That is the phase
boundary between the high temperature rhombohedral and tetragonal forms is, practically
speaking is a vertical line. As in figure2.1, the piezoelectric activity peaks in the region of
14
the MPB composition and considerable effort has been directed to elucidating the reasons
for this technically very important phenomena.
Figure 2.1: Phase Stability in the System Pb(Ti1-x Zrx)O3 [5]
The current understanding is that the MPB is not a sharp boundary but rather a
temperature dependant compositional range over which there is a mixture of tetragonal
and monoclinic phases. At room temperature (300K) the two phases coexist over the
range 0.455≤ x ≤0.48. The enhanced piezoelectric activity of the commercial
compositions (x=0.48) can be rationalized in terms of the relatively large ionic
displacements associated with stress (electrical or mechanical) induced rotation of the
monoclinic polar axis.
Coupling coefficient and permittivity values across the PZT has been shown in Fig.2.2
15
Figure 2.2: Coupling Coefficient kp and Permittivity εr Values Across the PZT
Compositional Range
Depoling can be achieved by applying a field in the opposite direction to that used
for poling or in some cases by applying a high ac field and gradually reducing it to zero,
but there is a danger of overheating because of high dielectric loss at high fields. Some
compositions can be poled by applying a compressive stress (10-100 MPa). Complete
depoling is achieved by raising the temperature to well above the Curie point and cooling
without a field.
Aging effects are known to be significantly changed when the concentration of
vacant oxygen sites is increased either by doping or by heating in mildly reducing
atmospheres. The dipoles then provide an internal field stabilizing the domain
configuration thereby reducing ageing rate. The material features extremely large
dielectric constants. These properties make PZT-based compounds one of the most
16
prominent and useful electroceramics. Commercially, it is usually not used in its pure
form, rather it is doped with either acceptor dopants, which create oxygen (anion)
vacancies, or donor dopants, which create metal (cation) vacancies and facilitate domain
wall motion in the material. In general, acceptor doping creates hard PZT while donor
doping creates soft PZT. In general, soft PZT has a higher piezoelectric constant, but
larger loss in the material due to internal friction. In hard PZT, domain wall motion is
pinned by the impurities thereby lowering the losses in the material, but at the expense of
a reduced piezoelectric constant. It is used to make ultrasound transducers and other
sensors and actuators, as well as high-value ceramic capacitors. PZT is also used in the
manufacture of ceramic resistors for reference timing in electronic circuitry. The
manufacturing process for high-voltage piezoceramic consists of following steps. The
manufacturing process for high-voltage piezoceramic starts with mixing and ball milling
of the raw materials. Next, to accelerate reaction of the components, the mixture is heated
to 75% of the sintering temperature, and then milled again. Granulation with the binder is
next, to improve processing properties. After shaping and pressing, the green ceramic is
heated to about 750 °C to burn out the binder. The next phase is sintering, at temperatures
between 1250 °C and 1350 °C. Then the ceramic block is cut, ground, polished, lapped,
etc., to the desired shape and tolerance. Electrodes are applied by sputtering or screen
printing processes. The last step is the poling process which takes place in a heated oil
bath at electrical fields up to several kV/mm. In this case the ceramic take on
macroscopic piezoelectric properties [8].
Piezoelectric ceramics are fabricated with powder preparation. Powder preparation and
powder calcining and sintering are the more important processes that influence the
17
material properties. The powder is then pressed to the required shapes and sizes.
Machining, electroding, poling and application of a DC field to orient the dipoles are the
more steps to induce piezoelectricity.
The most common powder preparation is the mixed oxide route. In this process, powder
is prepared from the appropriate stoichiometric mixture of the constituents’ oxide route.
In the case of lead zirconate titanate (PZT): lead oxide, titanium oxide, and zirconium
oxide are the main compounds. Depending on application, various dopants are used to
tailor the properties of interest. PZT ceramics are rarely utilized without the addition of
dopants to modify some of their properties. A-site additives tend to lower the dissipation
factor, which affects heat generation, but also lower the piezoelectric coefficients; for this
reason they are mostly used in ultrasonics and other high frequency applications, B-site
dopants increase the piezoelectric coefficients but also increase the dielectric constant
and loss. They are utilized as actuators in vibration and noise control, benders. Mixing of
the powders can be done by dry-ball milling or wet ball milling. Both methods having
advantages and disadvantages: wet ball-milling is faster than dry-milling; however, the
disadvantage is the added step of liquid removal. The most common method for making
PZT ceramics is through wet-ball milling; ethanol and stabilized zirconia media are
added for a wet milling process. A vibratory mill may be used rather than a conventional
ball mill; it was shown by Herner that this process reduces the risk of contamination by
the balls and the jar [9]. Zirconia media are used to further reduce the contamination
risks. The calcinations step is a very crucial step in the processing of PZT ceramics; it is
important that the crystallization be complete and that the perovskite phase forms during
this step. After calcining, a binder is added to the powder, and then the mixture is shaped
18
usually by dry-pressing in a die for simple shapes, or extrusion, or casting for more
complicated bodies. Next, the shapes are sintered: placed in an oven for binder burn-out
and densification.
The major problem in the sintering of the PZT ceramic is the volatility of PbO at about
800 0C. To minimize this problem, the PZT samples are sintered in the presence of a lead
source, such as PbZrO3, and placed in closed crucibles. The saturation of the sintering
atmosphere with PbO minimizes lead loss from the PZT bodies. Sintering can now be
carried out at temperatures varying between 1200-1300oC. Despite precautions, there is
usually a resulting loss of 2%-3% of the initial lead content.
After cutting and machining into desired shapes, electrodes are applied and a strong DC
field is used to orient the domains in the polycrystalline ceramic. DC poling can be done
at room temperature or at higher temperatures depending on the material and the
composition. The poling process only partially aligns the dipoles in a polycrystalline
ceramic, and the resulting polarization is lower than that for single crystals.
This processing technique presents many uncertainties and the presence of a wide number
of other fabrication techniques is an indication that there is a great need for the
production of reliable PZT ceramics with optimum properties and microstructure. One
problem often encountered is the deviation from stoichiometry. This problem is often due
to impurities present in the raw materials as well as the lead loss during the sintering
processes, which invariably results in substantial alternations of the PZT properties. As a
result, the elastic properties can vary as much as 5%, the piezoelectric properties 10% and
the dielectric properties 20% within the same batch [10]. Also, the piezoelectric and
dielectric properties generally suffer if there is any lack of homogeneity due to poor
19
mixing. It is important then that the constituent oxides be intimately mixed. In the method
described above, however, the constituents are solid solutions and it has been shown that
an intimate mixing of solid solutions is difficult if not impossible. More information on
the preparation of piezoelectric ceramics can be found by Moulson [8] and Jaffe [11].
2.7 Piezoelectric Crystal Classes
Of the thirty-two crystal classes, twenty-one are non-centrosymmetric (not having
a centre of symmetry), and of these, twenty exhibit direct piezoelectricity. Ten of these
are polar (i.e.. spontaneously polarize), having a dipole in their unit cell, and exhibit
pyroelectricity. If this dipole can be reversed by the application of an electric field, the
material is said to be ferroelectric [5].In a piezoelectric crystal, the positive and negative
electrical charges are separated, but symmetrically distributed, so that the crystal overall
is electrically neutral. The domains are usually randomly oriented, but can be aligned
during poling (not the same as magnetic poling), a process by which a strong electric
field is applied across the material, usually at elevated temperatures. When a mechanical
stress is applied, this symmetry is disturbed, and the charge asymmetry generates a
voltage across the material. Crystal is a solid in which the constituent atoms, molecules,
or ions are packed in a regularly ordered, repeating pattern extending in all three spatial
dimensions. Generally, crystals form when they undergo a process of solidification.
Under ideal conditions, the result may be a single crystal, where all of the atoms in the
solid fit into the same crystal structure. However, generally, many crystals form
simultaneously during solidification, leading to a polycrystalline solid.
20
Crystalline structures occur in all classes of materials, with all types of chemical bonds.
Almost all metal exists in a polycrystalline state; amorphous or single-crystal metals must
be produced synthetically, often with great difficulty. Ionically bonded crystals can form
upon solidification of salts, either from a molten fluid or when it condenses from a
solution. Covalently bonded crystals are also very common, notable examples being
diamond, silica, and graphite. Polymer materials generally will form crystalline regions,
but the lengths of the molecules usually prevent complete crystallization. Weak Van der
Waals forces can also play a role in a crystal structure; for example, this type of bonding
loosely holds together the hexagonal-patterned sheets in graphite. Most crystalline
materials have a variety of crystallographic defects. The types and structures of these
defects can have a profound effect on the properties of the materials. Some crystalline
materials may exhibit special electrical properties such as the ferroelectric effect or the
piezoelectric effect [8].
Following are few important piezoelectric types used in various applications
2.7.1 Lead Zirconate Titanate (PZT)
Lead zirconate titanate is a ceramic material that shows a marked piezoelectric
effect compared to other ferroelectric properties. PZT develops a voltage difference
across two of its faces when compressed (This is used for sensor applications), and
physically strained when an external electric field is applied (used for actuators etc). It is
also ferroelectric, in other words, it has a spontaneous polarization which can be reversed
in the presence of an electric field. The lead zirconate titanate is widely used in
polycrystalline (ceramic) from with very high piezoelectric coupling. Depending on the
formula of preparation, PZT materials may have different forms and properties.
Manufacturers of PZT use proprietary formulas for their products [12]. Techniques that
are commonly used for preparing the bulk PZT materials such as (PZT-4, PZT-5) are not
21
suited for micro-fabrication. A number of techniques for preparing PZT films have been
demonstrated, including sputtering, laser ablation, jet molding, and electrostatic spray
deposition [13]. Lead zirconate titanate shows a much greater piezoelectricity effect than
quartz. These can readily be fabricated into variety of shapes and sizes and therefore can
be tailored to a particular application [14].
2.7.2 Barium Titanate
Barium titanate is an oxide of barium and titanium with the chemical formula
BaTiO3. It is a ferroelectric ceramic material, with a photorefractive effect and
piezoelectric properties. It has four structures as a solid, starting with the high
temperature to a low temperature structure. These four structures are cubic, tetragonal,
orthorhombic, and rhombohedral crystal structure. All of the structures exhibit the
ferroelectric effect except for the cubic barium titanate structure. Barium titanate can be
manufactured by sintering of barium carbonate and titanium dioxide, optionally with
other materials for doping. Barium titanate is often mixed with strontium titanate. It has
the appearance of a white powder or transparent crystals and is insoluble in water and
soluble in concentrated sulfuric acid. As a piezoelectric material, it was largely replaced
by lead zirconate titanate, also known as PZT. Barium titanate crystals find use in
nonlinear optics. The material has high beam-coupling gain, and can be operated at
visible and near-infrared wavelengths. It has the highest reflectivity of the materials used
for self pumped phase conjugation (SPPC) applications. It can be used for continuous-
wave for wave mixing with milliwatt-range optical power. Barium titanate mostly used
as a dielectric material for ceramic capacitors, and as a piezoelectric material for
microphones and other transducers [15]
22
2.7.3 Polyvinylidene Fluoride (PVDF)
Polyvinylidene Fluoride, or PVDF is a highly non-reactive and pure thermoplastic
fluoropolymer. PVDF is very expensive; its use is generally reserved for applications
requiring the highest purity, strength, and resistance to solvents, acids, bases and heat.
Compared to other fluoropolymers, it is easier to melt because of its relatively low
melting point.
It is available as piping products, sheet, plate and an insulator for premium wire.
It can be injection molded and welded and is commonly used in the chemical,
semiconductor, medical and defense industries, as well as in lithium ion batteries. When
poled, PVDF is a ferroelectric polymer, exhibiting efficient piezoelectric and pyroelectric
properties. These characteristics make it useful in sensor and battery applications. PVDF
has a glass transition temperature (Tg) of about -350C and is typically 50-60% crystalline.
To give the material its piezoelectric properties, it is mechanically stretched to orient the
molecular chains and then poled under tension. Polyvinylidene Fluoride is a synthetic
floropolymer with monomer chains. It exhibits piezoelectric, pyroelectric and
ferroelectric properties, excellent stability to chemicals, mechanical flexibility and
biocompatibility [16].
2.8 Recent Developments in Piezoelectric Ceramics
There has been a growing interest in recent years in piezoelectric ceramics
materials because of their excellent dielectric, sensing, actuating and efficient process
control applications. Lead zirconate titanate (PZT), barium titanate (BaT1O3), lead
metaniobate (PbNb2O6) and polyvinylidene fluoride (PVDF) polymers are generally
favored as smart sensing materials. These materials are being used in critical engineering
23
systems and smart structures. Fatigue failure due to electrical and thermal shocking is a
major issue in degradation of these materials. A lot of work has been done in this area but
still various issues need to investigate. Recent developments and current issues in
piezoelectric materials and deterioration of their properties in different working
conditions have been discussed in a review paper titled “Recent Developments in
Piezoelectric Ceramics Materials and Deteriorations of their Properties” [Appendix-B].
The new piezoelectric finite element capability available in some commercial packages
like ANSYS makes it convenient to perform static, dynamic, transient and thermal
analysis for the fully coupled piezoelectric and structural response.
In the past two decades many theoretical studies including finite element analysis and
modeling have been conducted to the fracture and damage of piezoelectric ceramics
under electrical, mechanical or combined electromechanical loading modes. The decay of
piezoelectric properties and the degradation mechanisms of piezomaterials due to the
strong coupling effect of the high alternating electric field and mechanical load have been
serious concerns, but have not well characterized. In particular, durability performance of
peizomaterials, in terms of integrity and piezoelectric properties, is always a key issue in
long term for both conventional piezoceramic based actuation system and recently
developed new generation actuation systems. Cyclic domain switching in piezomaterials
caused by the high frequency cyclic electric field and consequently the electric field
induced fatigue crack growth, and the temperature rise due to self heating of the
materials, seriously deteriorate the electromechanical properties of piezomaterials [17].
Ferroelectric ceramics has a broad range of applications due to its enhanced physical
properties such as dielectric coefficients, elastic – optical coefficients, piezoelectric
24
coefficients, elastic coefficient. All these properties have been investigated [18-20].
There are considerable reports on experimental studies of fatigue induced either by an
electrical or a mechanical load alone [21]. Ferroelectric fatigue was a key problem for the
wide application of ferroelectric materials in non-volatile memories and other
electromechanical devices, such as actuator. Up to now, much work has been carried out
on the research towards understanding ferroelectric fatigue and thus many corresponding
mechanisms have been suggested [22].
In the ferroelectrics literature, the term fatigue generally refers to the gradual degradation
of bulk material properties, such as the saturation remnant polarization, in a cyclically
loaded specimen.
Experiments have shown that cracks grow in ferroelectric ceramics under cyclic electric
fields. The works of Jiang, Cross, and coworkers have shown that high porosity might
cause the severe decrease on polarization under alternating electric loading. Jiang et al.
(1993) have found from their experiments that the smaller the grain size the more
difficult it is to produce and propagate cracks. Jiang have studied the difference on the
electric fatigue behavior caused by conditions of ceramic-electrode interfaces [23, 24].
Hill et al. (1996) have used transmission electron microscopy (TEM) to observe the
fatigue behavior of PZT -8 by measuring acoustic velocity and piezoelectric coefficients
[25]. Tai and Kim have investigated the fatigue of PZT ceramics under cyclic
compressive loading by measuring piezoelectric coefficient and capacitance [26].
Recently, Jiang and Sun (1999) have studied the behavior of fatigue crack growth rates
under combined electrical and mechanical loads. They have attempted to use a single
energy parameter to quantify electrical and mechanical loads. They also had extended the
25
mechanical fatigue theory and have included an intensity factor of electric displacement
in the Paris law [27].
It is common practice to embed piezoelectric sensors into prototypes because these
sensors can be manufactured with strength and dimensional characteristics that do not
degrade the structural integrity of the materials of the prototype. When thermal effects are
generated through either friction or direct exposure to significant temperature gradients,
the reliability of the electrode layer in these piezoceramics can completely dominate the
performance of the device being investigated [28]. A new 3-D electromechanical-coupled
field finite method has been proposed to accurately predict the resonant frequency and
harmonic response of a system applying the step voltage as input. The simulation of
piezoelectric devices with time domain was modeled by Lerch (1990) [29].
2.9 Thermal Cycling and Shocking in Piezoelectric
Ceramic materials are brittle and susceptible to catastrophic fail under most
conditions of high heat transfer and rapid environmental temperature variations. Thermal
stress resistance of brittle ceramics can be measured by two methods. The first approach
is based on thermo elastic theory [30]. Material properties are selected to avoid the
initiation of fracture by the thermal stresses. In general this requires materials with high
values of tensile strength, thermal conductivity, and thermal diffusivity combined with
low values of thermal expansion coefficient, Young’s modulus of elasticity, Poisson’s
ratio and emissivity [31-33]. Some workers have reported a reasonable agreement
between calculated and observed thermal stress performance, providing a valid basis for
the thermo-elastic approach to thermal stress fracture [34, 35]. Thermal shock resistance
concerned with the extent of crack propagation and the resulting change in physical
26
behavior of the material. Thermal stress resistance may be determined by the relative
change in strength, the loss of weight, or the change in permeability. The change in
elastic behavior or resonant frequency may also be used as a measure of thermal stress
resistance. A new approach to the calculation of the extent of crack propagation in brittle
ceramics as a function of thermal shock treatment has been presented by
D.P.H.Hasselman (1969) [36].
Heat transfer effects in ferro-electric materials, electric impact loading, thermal effects of
piezoelectric sensors and heat generation rate in piezoelectric materials have also been
investigated. Ningning Dul (2006) investigated the energy dissipation mechanisms and
thermal effects in cracked piezoelectric materials [37]. His results showed that the
temperature rise caused by electric saturation or electric impact loading is remarkable and
may play a significant role in fracture of piezoelectric materials especially under
high frequency condition and some electric-waves with higher electric loading rates.
Many piezoelectric structural components are under the influence of transient thermal
loads like in aerospace structures and hence it is necessary to accurately model the
coupled thermal-mechanical-electrical behaviors of piezoelectric ceramics. In thermal
shock conditions during sudden heating or cooling of a solid, development of high
values of stresses are possible. If the thermal transient is severe enough, sudden fracture
may occur. Thermal shocks in a plate of finite thickness have been attempted. A fracture
mechanics analysis having an edge crack in the transient stress analysis, and the degree
of severity of any given thermal shock is characterized in terms of the stress-intensity
factor [38, 39]. The dynamic linear piezothermoelastic theory, the constitutive
formulations, and governing equations for thermal, elastic, and electric fields have been
27
discussed [40, 41]. The effective thermal expansion and pyroelectric coefficients of
piezoelectric composites have also been analyzed [42]. The transient thermo-electric-
elastic fields in a hexagonal plate were investigated by Choi et al [43]. Recently,
numbers of coupled thermal-mechanical-electrical finite-element method are being used
to study thermally induced stresses in smart structures. The phenomenon of strength
evaluation of piezoelectric ceramics under transient thermal environment has also been
investigated [44].
Piezoelectric thin films operating in many structural components, like in aerospace
component, are sometime subjected to severe thermal loading which may be produced by
aerodynamic heating, by laser irradiation, or by localized intense heating. The amount of
energy delivered to the thin film surface in short time plays a significant role in
developing thermal stresses. Thermal shock and thermal fatigue of ferroelectric thin film
were investigated by the pulsed laser tests by Zheng et al [45]. Micrographs from
scanning electron microscope show a remarkable difference in microstructure and grain
size after during thermal cycling. They also discussed the possible origins of the thermal
fatigue cracks. Thermal shocks in a plate of finite thickness have been attempted.
Thermal shock and thermal fatigue of ferroelectric thin film were investigated by the
pulsed laser tests by X.J.Zheng et. al. (2005)
Lead zirconate titanate decreases the dielectric constant and the resonance frequency by
thermal shock. Temperature stability for dielectric constants and resonance frequencies is
an important phenomenon. Tolerance to thermal shocks is strictly required in piezoelectric
resonators and filters. Resonance frequency of vibration mode has also been investigated
earlier [46].
28
Fatigue studies shows that material degradation is strongly influenced by temperature and
by the electromechanical fatigue. Temperature plays an important role in dictating the
electromechanical response of piezoelectric materials. In typical actuators, the operating
temperature is less than 100C0 and work show that the relative permittivity varies linearly
with temperature up to 120C0 and it shows that linear approximation of relative
permittivity with temperature is valid. Behavior of piezoelectric ceramics used in actuator
application was discussed by Donny Wang and his fellows [47]
The extent of aging has been expressed as total normalized frequency change over a
specific time period. Aging mechanism and high frequency modes of piezoelectric
resonator was earlier analyzed [48].
Thermal shock resistance of the materials was evaluated by water quenching and a
subsequent three point bending test to determine flexure strength degradation. In the
investigation it was analyzed that fracture toughness can be improved. By considering
specific heat treatment the ceramics materials can be shock resistance [49].Transient
thermal analysis of thin strips used in various applications had been investigated since
long. Thin strip with or without crack was determined for its behavior in transient thermal
environment [50].
The ageing process in any ceramic can be accelerated by exposing the ceramic to high
mechanical stress, strong electric depoling field and high temperature approaching the
Curie point. Most of the properties of piezoelectric ceramics changes gradually with time.
The changes tend to be logarithmic with time after poling. The ageing rate of various
properties depends on the ceramic composition and on the way the ceramic is processed
during manufacture. Because of ageing, exact values of various properties such as
29
dielectric constant, coupling, and piezoelectric constants may only be specified for a
standard time after poling. The longer the time period after poling, the more stable the
material becomes.
2.10 Effect of Water and Moistures in Piezoelectric Ceramics
Transient thermal analysis of thin strips has been studied [50]. Piezoelectric thin
films operating in many structural components such as in aerospace applications can
experience severe thermal loading which may be produced by aerodynamic heating, laser
irradiation, or incidental heating from other electrical components. The amount of energy
delivered to the thin film surface in a short time plays a significant role in developing
thermal stresses. Recently Jiang et. al (2006) studied the effect of water induced
degradation on soft PZT piezoelectric ceramics using electromechanical charging in a
NaOH solution. They observed the effect of electrolysis of water on property changes of
the PZT [51]. Other researchers have studied the affect of applying a 50Hz AC voltage on
the degradation in properties of a PZT ceramic ring in NaOH solution. The rings treated
with AC voltage were found to degrade in material properties [52].
As the performance of PZT materials used in various applications may be affected by
changes in temperature and water condition, therefore, in this study the effect on
performance of a PZT material have been analyzed at different frequencies in different
water conditions.
Ceramic materials are brittle and susceptible to catastrophic failure under conditions of
rapid environmental temperature variations [30]. Relative change in strength, the loss of
weight, or the change in permeability, the change in elastic behavior or resonant
30
frequency is the measure of thermal stress resistance [36]. Thermal shocks in a plate of
finite thickness have been attempted. Fatigue studies show that material degradation of
PZT ceramics are strongly influenced by temperature and by the electromechanical
fatigue. Lead zirconate titanate ceramics shows a decrease in dielectric constant and the
resonance frequency when subjected to thermal shock. Thermal shock resistance of the
materials was evaluated by water quenching and a subsequent three point bending test to
determine flexure strength degradation. Degradation of various properties of the piezo
devices in the presence of water & AC voltage was investigated and concluded that water
is an important cause for the degradation of PZT piezoelectric ceramics [52].
Dielectric constant is an important parameter, especially in the piezoelectric device such
as resonators and filters used in the electronic circuits. Impedance is also dependent on the
dielectric constant of the piezoelectric. Currently there is limited data available for the
thermal shocking and quenching effect of a thin PZT disc. Therefore there is a scope to
investigate various parameters which are still unattended. In this research work, the focus
is to investigate the degradation of thin PZT disc due to thermal shocking and its
quenching effect. A noticeable change in capacitance and dielectric constant has been
observed which is further changing other piezoelectric properties.
By considering all of the above discussions, it is concluded that fatigue behavior of
piezoelectric ceramics materials either by electrical, mechanical, electromechanical has
been investigated extensively, whereas there is a scope of work during thermal
cycling/shocking of piezoelectric material in variable conditions. In chapter 4
experimentations performed, analyzed and comprehensive discussions have been
presented.
31
CHAPTER#03
EXPERIMENTAL METHODOLOGIES
3.1 Introduction
The difference between environmental and cyclic induced fatigue is not very well
clear and some ceramics materials show combination of both. Some standard existing
methodologies particularly for mechanical testing have been studied extensively. In the
present work thermal cycling/shocking of thin PZT disc has been experimentally studied
by using relevant instrumentations. Experimental arrangement for this research work has
been briefly described here and will be elaborated in next chapter. Reliability has been
assured by calibration and by repeatability. Calculations of piezoelectric parameters are
based on IEEE standard on Piezoelectricity [53].
This chapter demonstrates the testing methodologies, selection of specimen and design of
experiments. A self designed and fabricated circuitry for the determination of frequency
of maximum and frequency of minimum impedance has also been demonstrated. The
methodology for the determination of elastic, piezoelectric, and dielectric constant has
been done by using resonance method. A brief description of the experimentations phases
performed for this particular research has also been described.
3.2 Standard Fatigue Testing Methodologies
Ceramics and Glasses subjected to static or cyclic loads exhibit time-dependent failure
due to the growth in inherent and induced flaws to a critical size. Cyclic loading is not
required to generate crack extension. Hence some time the phenomenon is also referred
32
to as “static fatigue.” The phenomenon is also referred to as stress corrosion, delayed
failure, slow crack growth or environmentally induced fatigue. In addition to an
environmentally induced, stress corrosion mechanism, many ceramics materials exhibit
enhanced fatigue crack growth during cyclic loading. Factors such as grain size and grain
boundary phase, which generally relate to the toughening or environmental sensitivity,
influence the sensitivity to cyclic loading. Fatigue mechanisms in brittle solids can be
classified as environmentally induced fatigue or as cyclic fatigue. Environmentally
induced, or static, fatigue in ceramics is chemically activated atomic reaction that is
enhanced by stress and temperature [54].
3.3 Thermal Cyclic Loading in Piezoelectric Ceramics
Due to wide range of operating conditions and applications for the systems under
development, careful consideration must be given to the selection of piezoelectric
materials. The selection of material becomes more important when they are used for wide
range of operating temperatures. The current research work is focused to thoroughly
investigate the characteristics of thin PZT disc in various cyclic and shocking
environments. Thermal shock conditions due to sudden heating and cooling of the solids
can develop very high stresses. The effect of these stresses becomes sensitive when the
disc size is too small as selected for the present work. The degree of damage and strength
degradation of ceramics subjected to severe fluctuating thermal environments plays a
significant role in relation to service requirements and lifetime performance. The coming
articles are to demonstrate the selection of specimen, instrumentation and methodologies
for the measurement of few piezoelectric properties.
33
3.4 Selection of Specimen
Thin discs of lead zirconate titanate specimen described in Table.3.1 have been
selected for experimentation, Parent properties of specimen are described in Table.3.2.
PSI-5A4E is an industry type 5A (Navy Type II) piezoceramic. Thin vacuum sputtered
nickel electrodes produce extremely low current leakage and low magnetic permeability.
It operates over a wide temperature range and is relatively temperature insensitive. DOD
TypeII, Lead-Zirconate Titanate having high strain (charge) constants, permittivity, and
coupling constants. Its mechanical quality factor is low with high Curie temperature
which extends its temperature range and thermal stability.
High charge output useful for sensing devices and generator elements.
High strain output useful for large displacements at modest voltages.
The particular selected type is used for sensing devices like, receivers, knock, acoustic,
musical pick-ups, vibration, vortex, material testing and for actuators like valves,
positioning, vibrating, fans, tilters etc.
Table.3.1: Description of Specimen (PSI-5A4E Single Layer Disks) Composition Trade (Dimension)
Diameter Thickness Part No
Lead Zirconate Titanate PiezoSystems Inc. 12.7mm 0.191mm T107-A4E-273
34
Table.3.2 Parent Specimen Properties as provided by supplier (PIEZO SYSTEM INC. USA).
Piezoelectric Properties Sr #
Description Notation Value Units
01 Relative Dielectric Constant @1KHz
KT3 1800
02 Piezoelectric strain coefficient d33 390 x10-12 Meters/Volt 03 d31 -190 x 10-12 Meters/Volt
04 Piezoelectric voltage coefficient g33 24 x 10-3 Volt meters/Newton
05 g31 -11.6 x 10-3 Volt meters/Newton
06 Coupling coefficient K33 0.72 07 k31 0.32 08 Polarization field Ep 2 x 106 Volts /meter 09 Initial depolarization field Ec 5 x 105 Volts/meter Mechanical 10 Density Ρ 7800 Kg/meter3 11 Mechanical Q Q 80 12 Elastic modules YE
3 5.2 x 1010 Newtons/meter2 13 YE
1 6.6 x 1010 Newtons/meter2 Thermal 14 Thermal expansion coefficient ~ 4 x 10-6 Meters/meter oC 15 Curie Temperature 350 oC
3.5 Resonance Method
All electronics materials have their own resonance frequency on which they
resonate. When exited at this resonant frequency, fn, the body will resonate freely with
greater amplitude than at other frequencies. In spite of resonant frequency there is an
anti-resonant frequency, fm, where the impedance of the body is at a maximum and the
oscillation amplitude is at a minimum. The measurement of these characteristics
frequencies provides the means to evaluate the piezoelectric and elastic properties of the
ceramic. There are different modes of vibration of the ceramic, such as thickness or
planar mode and other is extensional or longitudinal mode. The resonant frequency is at
35
the point of minimum impedance and the anti-resonant frequency is at the point of
maximum impedance.
At resonance, a piezoelectric element may be modeled by the equivalent circuit. This
circuit is commonly referred to as Van Dyke’s Model and is recommended by the IEEE
Standard on Piezoelectricity [53]. Resonance must be sufficiently isolated from other
modes to eliminate the effects of any adjacent modes. To assure isolation of the
resonance, sample geometry must be chosen carefully. Fixturing of the sample should not
impose any constraints on the vibration of the ceramic. This can be accomplished by
using a point holder positioned at a node of vibration. Also, all leads should be shielded
up to the contact point as much as possible to avoid any stray capacitances which may
arise. Several circuits to measure fm and fn of piezoelectric ceramic have been proposed
[55-57]. The dielectric properties of a piezoelectric vibrator are dependent on the elastic,
piezoelectric and dielectric constant. The above stated properties can be measured by
using suitable size and shape of the specimen is specific orientation. The measurements
are basically consists of determining the electrical impedance of the resonator as a
function of frequency. In particular capacitance of the selected specimen has been
determined at resonance and anti resonance frequencies and respectively the change in
dielectric constant and coupling factor has also been measured.
3.5.1 Measurement of Material Properties
Measurements of capacitance are usually carried out at 1 KHz and at low
excitation voltages (mV level). Although research has shown capacitance and loss to vary
with excitation voltage and frequency [58, 59], the 1KHz, low voltage measurement is
36
used in the determination of material properties. The free relative dielectric constant, K3T,
is defined as the ratio of the permittivity of the material to the permittivity of free space.
It is calculated from the following equations [53, 55]. Equation 3.1 is the measure of
dielectric constant of the material.
TK3 = A
tC0ε
(3.1)
Where t is the distance between electrodes in meters, C is the capacitance in farads, ε0 is
the permittivity of free space (8.85 x 10-12 F/m), and A is the area of an electrode in
meters2.
The loss tangent, tanδ, is defined as the ratio of resistance to reactance in the parallel
equivalent circuit. It is a measure of the dielectric losses in the material and therefore also
a measure of the heat generation capacity of the ceramic when operated under dynamic
conditions. This is a direct measurement and is usually formed at the same conditions as
the capacitance measurement.
The three most common coupling coefficients are kp, k31, and k33; where the p is for
planar, and the 31 and 33 subscripts are for length extensional and thickness extensional
modes. The coefficients k33 and k31 can be calculated from the frequencies of minimum
and maximum impedance by using the equations 3.2 &3.3.
−+
−
−+
=
m
mn
m
mn
m
mn
fff
fff
fff
K)(
1
2)(
tan)(
1
2233
ππ
(3.2)
37
=231K
ψψ+1
(3.3)
Where
ψ =
−+
m
mn
fff1
2π tan ( )
−
m
mn
fff
2π (3.4)
The planar coupling coefficient kp (Eq 3.5) is defined for thin discs and can be
approximated by.
2
22
n
mnp f
ffK −= (3.5)
Elastic compliance is the ratio of a material’s change in dimensions (strain) in relation to
an externally applied load (stress). This is the inverse of Young’s modulus. For a
piezoelectric material, the compliance depends on whether the strain is parallel or
perpendicular to the poling axis and the electrical boundary conditions. Elastic constants
are calculated from the following equations 3.6, 3.7, 3.8, &3.9.
2233 41
lfS
n
D
ρ= (3.6)
233
3333 1 K
SSD
E
−= (3.7)
2211 41
wfS
m
E
ρ= (3.8)
38
ED SS 1111 = ( )2311 K− (3.9)
Where ρ is the density of the material in kg/m3 and l is the distance between electrodes
and w is the width of the ceramic. The superscripts D and E stand for constant electric
displacement (open circuit) and constant electric field (short circuit) respectively.
The dij piezoelectric constants, which relate the applied electric field to the strain, can be
calculated from the coupling, elastic coefficients and the dielectric constant.
The gij piezoelectric constants are related to the dij coefficients and can be measured by
equations 3.10, 3.11, 3.12, &3.13.
ET SKKd 33303333 ε= (3.10)
ET SKKd 11303131 ε= (3.11)
TKdg
30
3333 ε
= (3.12)
TKdg
30
3131 ε
= (3.13)
It should be noted that the piezoelectric coefficients calculated above are only valid at
frequencies well below resonance and do not account for any non-linear behavior of the
ceramic.
39
The mechanical QM, the ratio of reactance to resistance in the series equivalent circuit is
given by equation 3.14.
−
= 22
2
21
mn
n
mmM ff
fCZf
Qπ
(3.14)
The familiar dielectric, elastic, and Piezoelectric constants for Piezoelectric ceramics may
readily be measured employing the proposed experimental setup by finding the minimum
and maximum frequencies.
3.5.2 Density Calculation
The density in Kilograms/ meter3 can be calculated, if required by using the
relationship as under.
Density ρ = weight in Kilograms/volume in m3
ρ = mass in air in Kilograms/(weight in air- weight in water) in Kilograms
3.5.3 Calculation of Free Relative Dielectric Constant K3T
In this work dielectric constant was measured by using the value of capacitance in pF and
physical dimensions of the specimen by using Equation 3.1.
KT3 = Distance between electrodes (m) x C (pF)/Area of one electrode (m2) x 8.85
3.5.4 Calculation of Coupling
Coupling is calculated from the frequencies of minimum and maximum
impedances. The frequencies of minimum and maximum impedances are not the exact
40
frequencies required for these calculations, and a small correction theoretically should be
made. However, when dealing with Barium Titanate and Lead Zirconate-Lead Titanate
compositions, the error resulting from omitting the correction is not significant, and
therefore can be ignored here.
3.6 Determination of Elastic, Piezoelectric, and Dielectric Constants
The elastic, piezoelectric, and dielectric properties of a piezoelectric material are
characterized by knowledge of the fundamental constants referred to a rectangular
coordinate system fixed relative to the crystallographic axes. A determination of these
fundamental constants requires a series of measurements on samples of various
orientations. There are a number of specific sample geometries and experimental
techniques that one can use to make the measurements. The choice of which techniques
to employ is subject to many considerations such as the size and shape of samples and the
instrumentation available. It is therefore not desirable to specify a single technique for
measuring piezoelectric materials. The quantities actually measured nevertheless must be
related to the fundamental elastic, piezoelectric, and dielectric constants by procedures
that are theoretically sound [53]
3.7 Selection of Experimental Setup/ Design of Experimentation
Complete experimental setup to perform experimentations was required. Experimentation
was designed by considering the size and shape of the specimen. Another consideration was to
consider the available experimental facilities for testing and measuring. Experimentation was
designed for thermal cycling and shocking conditions to analyze various effects and
characteristics of the selected specimen.
41
The research work divided into three phases and different instrumentations for testing and
measurements were selected. Care must be taken in the reliability of the instruments and their
functioning.
Instrumentation used for current research work has been listed below. The purpose was to
investigate the real time performance of piezo disc in different water conditions at
variable parameters, investigating thermal shocking effect in de-ionized water from
different temperature differences and at variable frequencies and resistances.
3.7.1 Phase-1: Performance of PZT and its Effect due to Water.
1. Function generator.
2. Oscilloscope.
3. Decade resistance box.
4. Hot plate.
5. Thermometer.
6. pH value measuring meter.
3.7.2 Phase-2 Thermal Cycling/Shocking Effect of Thin PZT Disc
1. Thermal chamber.
2. Thermocouple
3. Impedance analyzer
4. Capacitance measuring test fixture
5. Connecting wires and other accessories.
42
3.7.3 Phase-3 Thermal Cyclic Effect. (At Variable Frequencies and Resistances)
1. Function generator.
2. Oscilloscope.
3. Decade resistance box.
4. Thermal chamber.
5. Thermocouple
3.8 Research Contribution
The required experimentation has been done in three phases and briefly described
in under headings. Detailed description of experimental setup, experimentation and
analysis of results of each phase has been elaborated in chapter 4.
3.8.1 Phase-1: Performance of PZT Disc and its Effect Due to Water.
To understand the philosophy of thin PZT disc in hot water environment and its effect on
output Peak-Peak voltage has been analyzed. The experimentation was designed
accordingly.
This phase performed in three different water conditions as under.
• In simple water
• In de-ionized water
• In NaCl solution
3.8.2 Phase-2: Thermal Cycling/Shocking Effect of Thin PZT Disc
• Thermal shocking from 1000C from thermal chamber to de-ionized water
at 200C.
43
• Thermal cycling test between 1000C and 900C for 60 cycles in step of 10
cycles.
• Thermal cycling test between 1000C and 900C for 60 cycles continuous.
• Thermal shocking from 1500C from thermal chamber to de-ionized water
at 200C.
3.8.3 Phase-3: Thermal Cyclic Effect. (At Variable Frequencies and Resistances)
• At room temperature (200C)
• At 1600C
3.9 Measurements
Phase-1 contributes in determining the output voltage across thin PZT soldered
disc, which determine its sensitivity of output voltage in water due to temperature change
and its effect with respect to variable frequencies and resistances. In phase-1
experimentation, soldered disc was connected with designed circuitry to have the output
peak-to-peak voltage for four selected frequencies. In this part of work, output
performance in the form of Pk-Pk voltage and its effect on thin disc was determined.
Detail will be described in Chapter-4
Phase-2 comprises a comprehensive analysis of cyclic and shocking of PZT thin disc in
thermal environment. By using the experimental results, piezoelectric, mechanical and
physical parameters can be calculated by using the appropriate relationships. In this phase
disc was thermally cycled for specific temperature range and shocked in de-ionized
water. Detail will be described in Chapter-4. Focus of this part of work is only to
determine the change in coupling factor, dielectric constant, and impedance during
44
thermal cycling and shocking of lead zirconate titanate ceramics disc. Due to very small
size of the specimen, the effect of density is supposed to be negligible and therefore not
considered in the calculations.
Phase 3 experimentation was performed in thermal chamber environment. The effect of
temperature with respect to variable frequencies and resistances on its output peak-peak
voltage was analyzed. This part demonstrates the sensitivity of the disc by changing the
above variables in thermal environment. Detailed analysis has been demonstrated in
chapter 4.
3.10 Capacitance measurement by 6451B Dielectric Test Fixture
Dielectric test fixture was attached with impedance analyzer to measure various
parameters during thermal cycling and shocking of PZT disc.
3.10.1 Specifications
These specifications are the performance standards and limits against which the selected
instrument is tested. The function of the fixture is to measure the dielectric constant and
dissipation factor without connecting the solid materials to the unknown terminals. The
specifications are as under.
Frequency range ≤ 15 MHz
Applicable voltage range ± 42 V peak max
Cable length = 1m
Operating temperature 00C to 550C
Operating Humidity ≤ 95% RH (400 C)
Weight = 3.7 Kg (Including accessories)
45
3.10.2 Performance Characteristics
Accuracy of performance characteristics vary with measurement conditions. However
16451B can measure dielectric constant in the range of 1 to 200,000 with an accuracy of
±1% and dissipation factor from 0.000001 to 9.99999 with an accuracy ± (5% + 0.005)
3.10.3 Selection of Electrodes
Four different types and sizes of guarded/guard electrodes are available with the
instrument kit. The selection of these electrodes for measurements depends on the size of
the specimen and measuring condition. Table 3.3 describes the dimensions and function
of the electrodes.
Table 3.3 Description of various electrodes and their selection
Sr # Electrode Description
01 Electrode-A Guarded/guard electrode with 38mm diameter used to
measure a material without thin film electrode.
02 Electrode-B Guarded/guard electrode with 5mm diameter used to
measure a material without thin film electrode.
03 Electrode-C
(For large thin film
electrodes)
Electrode used to measure a material which already have
thin film electrodes applied and consists of a guarded/guard
electrode.
04 Electrode-D
(For small thin film
electrodes)
Electrode used to measure a material which already have
thin film electrodes applied and consists of a guarded/guard
electrode.
46
3.10.4 Operation
The 16451B fixture assembly is equipped with a 4-terminal pair cable assembly,
guarded/guard electrodes, and a micrometer to set the distance between the electrodes. It
is recommended that large knob of micrometer should not be used to bring the
guarded/guard electrode into contact with the unguarded electrode or test material.
Dielectric measurement basically obtained by measuring the capacitance of a solid test
material. Three measurement methods are used by the instrument but we used the
contacting electrode method with thin film electrode. Suitable test material and suitable
electrode is necessary for accurate results.
3.10.5 Contacting Electrode Method (Used with thin film electrode)
This method uses thin film electrode applied on the test materials. Contacting electrode
method with thin film electrodes can be used for those materials on which thin film
electrode can be applied without changing its characteristics. This method is relatively
simple and uses simple equation to calculate dielectric constant. Error caused by air gap
between the electrode and surface of the test material is less in this case. The 16451B
provides two applicable electrodes, Electrode-C and Electrode-D for contacting electrode
method for thin film electrode with respect to size of the test materials.
3.10.6 Testing Material
To eliminate the error in measuring dielectric constant, the specimen should be according
the dimensions as specified by the testing equipment. The shape of the test material for
the 16451B should be a plate or a film. The applicable size of the test material should be
greater than the inner diameter of the guard electrode. It is recommended not to measure
47
a material whose diameter is much greater than the unguarded electrode. Doing this can
overload electrode and may damage it. To get accurate and better results, it is better to
use larger diameter and thinner thickness of the test material. Thickness of test material
should be accurate to get accurate results. Thickness of testing material is limited up to
10mm. The surface of the test material must be flat at all point. Thin film electrodes can
reduce the air gap between an electrode and a test material. Therefore the air film error
using thin film electrodes is less than one using rigid metal electrodes.
3.10.7 Error Corrections
To reduce the residual impedance and to measure the accurate dielectric constant, error
correction needed with the text fixture. For this purpose open and short corrections are
performed. For thin film electrodes, short correction is performed using electrode-C and
electrode-D. Load correction is performed to reduce error, such as negative dissipation
factor that can not be reduced by open and short correction.
3.10.8 Electrode Adjustment
Electrode adjustment of guarded/guard electrode is also necessary for accurate
measurement to check electrode parallelism. There are two types of adjustments, one is
rough adjustment that visually adjusts the electrode and the other is an accurate
adjustment that electrically adjusts the electrode using an LCR meter.
3.10.9 Measurement Procedure
Following steps are performed for the measurement.
1. Select the appropriate size and shape of the specimen with thin film electrodes.
2. Connect the text fixture to the impedance analyzer.
3. Set up the instrument to measure capacitance and dissipation factor (Cp-D)
48
4. If changing electrodes, perform the adjustment of electrode as described earlier.
5. Perform an open and short correction.
6. Set the test material between the electrodes.
7. Measured values of Cp and D by impedance analyzer will be used in the following
equations to calculate dielectric constant and dissipation factor.
rε =0.
.εACt pa
Where
Cp Equivalent parallel capacitance [F]
D Dissipation factor
ta Average thickness of test material [m]
A Area of guarded electrode [m2]
εo = 8.854 x 10-12 [F/m]
εr Dielectric constant of test material
It is recommended that measure three or more reading for take average for
reliability and accuracy.
3.11 Designed Circuitry for Frequency Determination
Experimental determination of frequency of maximum and minimum impedance
was one of the major parts of the research. Provision of an appropriate experimental
arrangement was a challenging job at local university and even there was no provision to
do required experimentation in any other organization. After having a comprehensive
literature review it was decided to have our own set up for the determination of frequency
49
of maximum and minimum impedance. A low cost experimental arrangement was
designed and fabricated [61]. A wave form signal generator has been used for the
generation of signals along with the designed circuitry.
The main parts of this setup are:
1. Switch box circuit 2. Oscillator circuit 3. Frequency counter 4. Decade resistor circuit 5. Voltmeter 6. Waveform generator
Fig.3.1 shows the designed circuit along with the connectors to measure the required parameters.
Fig-3.1 Self designed circuitry for the determination of fm and fn consisting of Switch box circuit, Oscillator Circuit & Decade resistor circuit
3.11.1 Switch Box Circuit
The circuit described in Fig.3.2 plays a central role in determining the desired
frequencies of maximum and minimum impedance. It has two types of selection
switches. Path control switch SW1 and the load resistance select switch SW2. Path
control switch SW1 is made by using a DPDT (Double pole double through switch). The
50
switch contains two sets of contacts that can be switched to connect to either of two
positions.
This switch selects one of the two paths i.e.. Specimen selection path and the decade
resistor path. When the switch is moved down then it selects specimen in the
measurement circuit. When the switch is moved up then it selects decade resistor in the
measurement circuit. The switch connects neither specimen nor decade resistor when it is
in the middle position.
Fig.3.2 Switch Box Circuit to determine the frequencies of maximum and frequency
of minimum impedance.
The switch box has an input signal which comes from the Oscillator card by using a
coaxial cable. Coaxial cable has a single copper conductor at its center. A plastic layer
provides insulation between the center conductor and a braided metal shield. The metal
shield helps to block any outside interference from fluorescent lights, motors, and other
components. In this case the coaxial cable is used instead of the normal two wire cable to
prevent undesired signal addition to the measurement circuit as this type of cable avoids
the signal attenuation due to the shielding present outside the copper connector. This
cable has another special addition which is made for the protection of the measurement
51
signal which is 100 ohms resistance connected at the input side of the cable. This resistor
limits the high values of current from flowing through the measurement circuit. Also
along with the 1 ohm resistor it forms a voltage divider circuit to increase the circuit
sensitivity.
Load resistance control switch SW2 is made in this circuit by using a 10- way position
switch. This switch can select any one of the nine resistance connected to the main
circuit. If the select position knob of any position is at the bottom level then the resistance
in that path is out of the main circuit while if the position knob is at the top level then that
path resistance would be entered into the main circuit as a load resistor. There are nine
different resistances available. Any one of these can be selected but only one value at a
time (Table 3.4).
Table. 3.4 Selection of Resistance in Switch-2 SW2 position 1 2 3 4 5 6 7 8 9
Resistor Value (ohms)
1 3.3 10 33 100 330 1000 3300 10000
Output signal from the main circuit is connected to a Voltmeter through a coaxial cable.
Again in this case coaxial cable is used for accurate measurements and fast data transfer.
This cable has no resistor as were placed in the input coaxial cable because to avoid any
loading effect to the coming measuring device i.e.. Multimeter. Loading effect reduces
the signal magnitude if there is a resistance comparable to the value of the voltmeter at
the output stage of the measuring setup. Both the input and output coaxial cables are
connected to the switch box circuit card by means of PCB mounted coaxial cable
connector. This is the most common type of connector used with coaxial cables and is
called the Bayone-Neill-Concelman (BNC) connector
52
Two 2-pin terminal blocks are also present in the switch box circuit. One terminal block
is for connecting the specimen to the switch box circuit and the other is for connecting
the decade resistor.
3.11.2 Oscillator Circuit
This circuit (Fig. 3.3) is made to produce a frequency signal of very low distortion in the
range of 10 to 200 KHz. Its design is based on the classic 555 timer circuit. It requires a
DC supply of more than 9 V to produce the required frequency signal. A three pin
terminal block is meant for connecting the DC supply with the correct polarities,
as indicated on the terminal block pins. To adjust the frequency of the oscillator circuit a
multiturn POT is used. When this POT is rotated in the clockwise direction, the
frequency of the signal increases while on rotating it counter clock wise decreases the
signal frequency. A 2-pin terminal block is present in the oscillator card to connect the
required frequency signal to the external setup.
Fig.3.3 Oscillator Circuit (frequency signal range10 to 200 KHz)
53
3.11.3 Frequency Counter
To measure the frequency produced by the oscillator circuit a frequency counter is
required. In this setup a very precise digital Multimeter with the frequency measuring
capability is used. For determining the frequency of counter circuit the positive (red) lead
of this digital Multimeter is connected to the positive (+) pin of the signal terminal block
at the oscillator card while the negative (black) lead of the digital Multimeter is
connected to the negative (-) pin of the same signal terminal block. While the position
selection switch of the Multimeter is positioned at the Hz position.
3.11.4 Decade Resistor Circuit
The decade resistor circuit box (Fig.3.4) is made to get precise resistor values
from 1 ohm to 111ohms. This circuit has two 10-way position selection switches which
are named as switch I and switch II. In switch I, we can have a resistor value from 1 ohm
to 10 ohms.
54
Fig.3.4. Decade resistor circuit Fig.3.5. Waveform Generator
The scheme of selection is that if the switch knob of any of the position is at the top level
then that resistor value will be selected and if the knob is at the bottom level then that
resistor will be out of the selection. But we can select only one position at a time. There is
also a three position selection switch which can select any of the two resistor values as
obtained from the switches I and II as in Table 3.5. While this switch is at the middle
position nothing is selected
Table.3.5 Selection of Resistance for Switch I & Switch II Switch I top position
1 2 3 4 5 6 7 8 9 10
Resistor value (ohms)
1 2 3 4 5 6 7 8 9 10
Switch II top position
1 2 3 4 5 6 7 8 9 10
Resistor value (ohms)
11 22 33 44 55 66 77 88 99 110
55
3.11.5 Waveform Generator
The waveform generator selected for the above stated setup is “Tektronics AFG
3021”, which is a 25 MHz single channel arbitrary waveform generator shown in Fig.3.5
having capability 1 mHz to 25 MHz Sine Waveform
3.11.6 Voltmeter A very sensitive digital Multimeter is used as a voltmeter in this setup for
determining a sharp change of the voltage values. The setup is completed to find out the
frequency of minimum impedance and the frequency of maximum impedance.
3.11.7 Frequency Measuring Procedure
1. Apply a waveform with waveform generator.
2. Turn switch 1 of the ‘switch box circuit’ to specimen.
3. Set switch 2 to 1 ohm i.e.. switch 2’s position 1 to ON and the remaining
positions 2 to 10 to OFF.
4. Set the waveform generator as:
Run Mode: Continuous
Function : Sine
Peak-to-peak output voltage: 5V
Channel: ON
Output: connected to the switch box using a coaxial cable
5. Slowly increase the frequency on the waveform generator from 1 Hz (i.e.. 1
Cycle/sec) to a value where a sharp maximum increase in voltage is obtained on
the ‘digital voltmeter’. If this sharp increase is not obtained then it will be
56
required to gradually increase the resistance from switch 2 i.e.. select position 2 to
ON and remaining 9 positions to OFF for selecting 3.3 ohms resistance and then
increase the frequency of waveform generator as described above. If the sharp
increase is not obtained then we will have to increase the resistance to 10, 33 or
100 ohms by selecting the corresponding switch 2 position to ON and the
remaining 9 positions to OFF. It is noted here that use the minimum possible
resistance to get the required change. In this way the frequency at which a sharp
increase in voltage is obtained will be the frequency of minimum impedance ‘fn’.
Read this value from the display of the waveform generator.
6. Now turn switch 2 to 1000 ohms i.e.. switch 2’s position 7 to ON and the
remaining 9 positions to OFF. Slowly increase the frequency from 1 Hz (i.e.. 1
Cycle/sec) to a value where a sharp decrease in voltage is obtained on the ‘digital
voltmeter’. If this sharp decrease is not obtained then it will be required to
gradually increase the resistance using switch 2 from 1000 ohms to 10000 ohms
then increase the frequency of waveform generator as described above. Again it is
required to get the desired response with the minimum possible selected
resistance. In this way the frequency at which a sharp decrease in voltage is
obtained will be the frequency of maximum impedance ‘fm’. Read this value from
the display of the waveform generator
An effort has been made to measure the frequency in the piezoelectric materials.
Development of a low cost experimental setup can be used for the demonstration to the
new researcher interested in this field. Fatigue behavior of piezoelectric ceramics
57
materials under various conditions definitely deteriorates the piezoelectric properties and
therefore the proposed setup is one of the basic needs to calculate frequency at maximum
and minimum impedance which are further used for calculating the other piezoelectric
parameters.
3.12 Measurement and Effect of Thickness by ANSYS
One of the most popular finite element software package ANSYS has the capabilities to
perform coupled field analysis. Piezoelectric materials can be simulated for their
particular geometry especially in this case the importance is to analyze the effect of
thickness for out put voltage with respect to load. The modeling, analyzing of these smart
scale components remained always a challenging job. A small effort in this regard has
been analyzed to determine the thickness effect in piezoelectric beam.A piezoelectric
cantilever beam analyzed for different thicknesses. Voltage change in each electrode
along with other related properties/parameters were found. Thickness variation produced
remarkable important results which can be used for optimizing the thickness range in
these smart materials. Voltage percentage per electrode determined and different nodal
solutions were obtained. Various recommendations have been suggested to analyze such
smart material before using in various applications for the generation and actuation
systems and for their reliability and durability [62] .
This chapter was all about the methodology adopted and about the instrumentation used
during experimentation. The self designed circuitry was an effort to design and fabricate
a low cost measuring instrumentation required for the frequencies determination. Due to
short range of this designed circuitry, the further experimentation has been performed by
using the instrumentation described earlier. in article 3.7.
58
CHAPTER # 04
EXPERIMENTATIONS AND ANALYSIS OF RESULTS
4.1 Introduction
Degradation in thin piezoelectric specimens occurs due to various cyclic loadings.
Such degradations may alter piezoelectric properties of materials. In chapter 3 the
research methodologies and brief description of experimentations was presented, whereas
the detailed experimentation, analysis of results and discussions has been elaborates in
the present chapter. Experimentations were performed in three different phases described
briefly in chapter 3. The aim of the experimentation was to observe that how
temperature/environment and medium influences the electrical and piezoelectric
properties of such thin piezoelectric specimens. It was observed that thermal cycling/
shocking affecting some critical characteristics of the material. These properties
definitely affect the performance of these materials. Various experimental phases have
been described below.
4.2 Phase-1: Performance Characteristics of a Lead Zirconate
Titanate Piezoelectric Ceramic Disc in Water.
Piezoelectric materials used in various sensing and actuating devices where they
may face various environmental conditions like moisture, and water. Degradation in
59
piezoelectric materials properties due to extensive electrical and thermal cycling is a
common phenomenon, which some time alter their internal characteristics. The
degradation in properties can affect the function and efficiency of instruments in which
these materials are being used. Therefore, it becomes important to identify the extent of
changes in performance when exposed to different types of solutions. A piezoelectric
ceramic disc was exposed to 3 different solutions, ordinary water, de-ionized water and a
solution of NaCl. The PZT was immersed in these solutions at 800C and performance
characteristics recorded on different frequencies. After effects of the immersed disc due
to three different solutions have been analyzed and it is observes that the PZT ceramic is
sensitive to the type of water, but regains its original performance characteristics within
short period of time. Out put peak-peak voltage is the performance parameter. In most of
the practical applications, the performances of piezoelectric materials are temperature and
frequency dependent. The intensity of temperature may change its internal characteristics
temporarily or permanently. Lead zirconate titanate (PZT) based ceramics are widely
used for their piezoelectric properties and these properties may degrade due to the
application of mechanical, electrical, electromechanical, and thermal cycling. A lot of
work is being carried out in exploring the behavior of these smart materials in electrical
and electromechanical loading conditions. Depolarization is one of the sources of
degradation, usually in those devices which undergoes a temperature rise during
operation. Performance of piezoelectric materials are affected by environmental factors,
including temperature, pressure, and humidity. It has been reported that the life time of
the piezoelectric devices decreases with the increase in temperature and humidity [63]. It
has been found that water facilitates the electro migration of silver electrodes along the
60
grain boundaries of piezoelectric ceramics [64]. Other studies showed that water
influences and causes of degradation in the presence of electricity [65]. In most practical
applications, the performance of thin PZT disc is dependent on temperature. The intensity
of temperature may change its characteristics permanently or it affect temporarily. For
this reason the temperature rise levels should be taken into consideration and studied in
depth [66].
Piezoelectric thin films operating in many structural components such as in aerospace
applications can experience severe thermal loading which may be produced by
aerodynamic heating, laser irradiation, or incidental heating from other electrical
components. The amount of energy delivered to the thin film surface in a short time plays
a significant role in developing thermal stresses. Thermal shock and thermal fatigue of
ferroelectric thin films were investigated by pulsed laser tests by Zheng et. al [67]. Water
induced degradation in lead zirconate titanate piezoelectric ceramics was studied before by
W.P.Chen et. al [68]. In 1996, Y.C.Chan et. al. [69] found that a thin water film can form
on the surface of ceramic components by condensation of aqueous vapor in air. In the
presence of voltage on such thin water film may cause degradation in piezo properties.
PZT materials are frequency and temperature dependent and it is observed that there is
slight decrease in the dielectric constant with the increase in frequency. Effect of
temperature and frequency on dielectric and ferroelectric properties has been investigated
[70]. Recently Jiang et. al studied the effect of water induced degradation on soft PZT
piezoelectric ceramics using electromechanical charging in a NaOH solution. They
observed the effect of electrolysis of water on property changes of the PZT [71]. Other
researchers have studied the affect of applying a 50Hz AC voltage on the degradation in
61
properties of a PZT ceramic ring in NaOH solution. The rings treated with AC voltage
were found to degrade in material properties [72]. Effect of heating rate on dielectric and
pyroelectric properties of PZT has been investigated by Mohiddon, et al. [73]. Other
researchers have studied the affect of applying a 50Hz AC voltage on the degradation in
properties of a PZT ceramic ring in NaOH solution. The rings treated with AC voltage
were found to degrade in material properties [74]. Effect of liquid in thin piezoelectric
plates has been studied earlier [75].
PZT instruments used in many environmental conditions and mediums like air, water, and
other chemical environments. The focus in this phase is to investigate the behavior of thin
disc in different water conditions at a temperature where it is under some excitation at
variable frequencies. Aftereffect of the water containments on the output peak-peak
voltage has been analyzed. The aim was to investigate the effect of water particles those
adhere to the surface of the disc on its performance characteristics.
4.2.1 Piezoelectric Material.
A piezoelectric single layer disc described in Table.3.1 was used for
experimentation. The disc was nickel electroded on its major faces and two wires were
soldered by using the compatible solder and flux. The parent properties of the
piezoelectric disc are described in Table.3.2.
62
4.2.2 Test Setup and Variables.
The tests were conducted in normal tap water having a pH value of 8.17, de-
ionized water having a pH value of 7.63 and in NaCl solution. A 5mg 99.5% pure sodium
chloride by Fluka Chemika was dissolved in 20ml de-ionized water to prepare a solution.
The water was placed in a container and heated by using a hot plate and approximately
kept constant at about 80oC with a variation of temperature ±1oC. The PZT specimen was
attached to an electric circuit consisting of function generator, decade resistor and
oscilloscope. The frequency input was developed by WAVETEK Model 273, 12 MHz
programmable sweep/function generator. The output peak-to-peak voltage was observed
by Tektronix TDS210 digital real time oscilloscope. The experimental setup is shown in
Fig-4.1.
Oscilloscope Decade Resistor Box
Computer Function Generator
Sample
Fig.4.1 Schematic Arrangement for the determination of Pk-Pk Voltage at variable frequencies
63
Output voltages were measured using four different frequencies generated by the function
generator. The selected frequencies were 50,100,150 and 200 Hz. The voltage across
Channel-1 and Channel-2 was 5Volts and 2Volts respectively and kept constant for all
measurements. A constant resistance of 110KΩ was selected from the decade resistance
box. Initial trend for output (peak- to-peak voltage) for selected frequencies measured in
air is shown in Fig-4.2. For this particular range of frequency input, the output voltage is
going to decrease.
5.32
8.48
7.46.28
0123456789
0 50 100 150 200 250Frequency (Hz)
Pk-P
k V
olta
ge (V
)
Fig-4.2. Variation of peak to peak voltage as a function of frequency.
First series of experimentation was performed in ordinary tap water with the frequency
set at 50 Hz and its corresponding output voltage in real time was observed by
oscilloscope and recorded. When the specimen was placed in hot water, its frequency
sharply decreased from 6.4V to 400mV. The PZT ceramic disc was placed in water at a
temperature of 80oC for 5 minutes and then taken out. The peak-to-peak voltage of the
64
PZT in air at room temperature 20oC was recorded and after the disc was immersed again
in the medium. Total ten such cycles were performed for each frequency (50, 100, 150
and 200 Hz). The total time for which the disc was immersed in water was about 50
minutes. This experimentation was repeated for de-ionized water and for the NaCl
solution. De-ionized water is similar to distilled water, in that it is useful for scientific
experiments where the presence of impurities may be undesirable. The lack of ions
causes the resistivity of water to increase. Ultra-pure de-ionized water can have a
theoretical maximum resistivity up to 18.31 MΩ·cm, compared to around 15 kΩ·cm for
common tap water. Further investigations were carried out to observe the after effects of
water on the peak to peak voltage with respect to time. After having the PZT disc to ten
thermal cycles for each frequency, the disc was placed in a vertical direction and allowed
to cool in still air at room temperature and a real time data was directly recorded for each
minute until the PZT surfaces were completely dry and the maximum output voltage at
particular frequency was obtained.
4.2.3 Results and Discussion
The response of the PZT ceramic during the heating and cooling (i.e. drying time)
of samples has been tabulated in Tables 4.1 to 4.17 and trends have been shown in Figs
4.3 to 4.8. The change in peak to peak potential values when the PZT ceramic was taken
out from water as a function of different frequencies, and when completely dried have
been shown in these figures. Tables 4.1 to 4.4 comprise the data obtained per minute for
heating cycle at 50, 100, 150 and 200 Hz frequencies in simple tap water. Values in each
case are taken twice and an average value has been considered for further discussion and
65
analysis. In general, the trend for peak to peak potential values recorded for the PZT.
When disc instantly taken out from ordinary water, de-ionized water and NaCl solution it
shows decrease in its original peak-peak values. The drop in potential in ordinary water
was different for the drop in other two water conditions. The drop in voltage is also
frequency dependent and clearly shown in Fig.4.3, Fig.4.5, and Fig.4.7.
Table 4.1 Heating time in ordinary water and respective voltage at 50Hz
Sr # H.T(Min) Pk-Pk (V) Pk-Pk (V) Avg Pk-Pk 1 0 8.48 8.56 8.52 2 5 3.52 4.06 3.79 3 10 3.12 3.28 3.2 4 15 2.48 2.72 2.6 5 20 2.56 2.88 2.72 6 25 2.32 2.48 2.4 7 30 2.16 2.24 2.2 8 35 2.08 2.16 2.12 9 40 2 1.92 1.96 10 45 1.84 2 1.92
Table 4.2 Heating time in ordinary water and respective voltage at 100Hz
Sr # H.T(Min) Pk-Pk (V) Pk-Pk (V) Avg Pk-Pk 1 0 7.44 7.52 7.48 2 5 2.32 2.48 2.4 3 10 2.16 2.24 2.2 4 15 2.16 2.32 2.24 5 20 2 2.08 2.04 6 25 1.92 2 1.96 7 30 1.76 1.82 1.79 8 35 1.84 1.92 1.88 9 40 1.76 1.92 1.84 10 45 1.76 1.84 1.8
66
Table 4.3 Heating time in ordinary water and respective voltage at 150Hz
Sr # H.T(Min) Pk-Pk (V) Pk-Pk (V) Avg Pk-Pk
1 0 6.24 6.4 6.32 2 5 1.92 2.08 2 3 10 1.92 2.16 2.04 4 15 1.76 1.84 1.8 5 20 1.6 1.68 1.64 6 25 1.6 1.76 1.68 7 30 1.6 1.76 1.68 8 35 1.6 1.68 1.64 9 40 1.6 1.68 1.64 10 45 1.6 1.52 1.56
Table 4.4 Heating time in ordinary water and respective voltage at 200Hz
Sr # H.T(Min) Pk-Pk (V) Pk-Pk (V) AvgPk-Pk 1 0 5.36 5.44 5.4 2 5 1.76 1.84 1.8 3 10 1.92 1.84 1.88 4 15 1.68 1.76 1.72 5 20 1.6 1.76 1.68 6 25 1.6 1.68 1.64 7 30 1.6 1.68 1.64 8 35 1.36 1.6 1.48 9 40 1.44 1.52 1.48 10 45 1.6 1.68 1.64
Table 4.5 Drying Time after taking out from ordinary water at 50Hz
Sr # Time(Min) Pk-Pk(V) Pk-Pk(V) Avg Pk-Pk 1 0 1.84 2 1.92 2 1 1.64 1.84 1.74 3 2 1.76 1.92 1.84 4 6 1.92 2 1.96 5 8 1.6 1.68 1.64 6 10 1.52 1.6 1.56 7 12 7.8 8 7.9 8 13 8.12 8.24 8.18 9 14 8.48 8.56 8.52 10 15 8.48 8.56 8.52 11 16 8.48 8.56 8.52
67
Table 4.6 Drying Time after taking out from ordinary water at 100Hz
Sr # Time(Min) Pk-Pk(V) Pk-Pk(V) Avg Pk-Pk 1 0 1.84 1.92 1.88 2 2 2 2.08 2.04 3 4 1.68 1.76 1.72 4 6 1.6 1.68 1.64 5 8 1.52 1.6 1.56 6 10 2.08 2.16 2.12 7 12 4 4.32 4.16 8 13 7.36 7.44 7.4 9 14 7.44 7.52 7.48 10 15 7.44 7.52 7.48 11 16 7.44 7.52 7.48
Table 4.7 Drying Time after taking out from ordinary water at 150Hz
Sr # Time(Min) Pk-Pk(V) Pk-Pk(V) Avg Pk-Pk 1 0 1.44 1.5 1.47 2 2 1.68 1.76 1.72 3 4 1.44 1.52 1.48 4 6 1.2 1.28 1.24 5 8 1.36 1.44 1.4 6 10 1.68 1.76 1.72 7 12 1.2 1.28 1.24 8 13 1.32 1.44 1.38 9 14 1.92 2 1.96 10 15 6.24 6.32 6.28 11 16 6.24 6.24 6.24
Table 4.8 Drying Time after taking out from ordinary water at 200Hz
Sr # Time(Min) Pk-Pk(V) Pk-Pk(V) Avg Pk-Pk 1 0 1.44 1.52 1.48 2 2 1.68 1.76 1.72 3 4 1.36 1.44 1.4 4 6 1.2 1.38 1.29 5 8 1.52 1.6 1.56 6 10 1.2 1.28 1.24 7 12 1.2 1.28 1.24 8 13 2 2.08 2.04 9 14 5.28 5.36 5.32 10 15 5.28 5.36 5.32 11 16 5.36 5.44 5.4
68
Table 4.9 Heating Time in De-ionized water and respective voltage at 50Hz
Sr # Time(Min) Pk-Pk (V) Pk-Pk (V) Avg Pk-Pk 1 0 8.56 8.64 8.6 2 5 5.76 5.84 5.8 3 10 5.12 5.2 5.16 4 15 5.04 5.2 5.12 5 20 4.72 5.04 4.88 6 25 5.04 5.52 5.28 7 30 4.88 5.36 5.12 8 35 4.96 5.36 5.16 9 40 4.96 5.28 5.12 10 45 5.36 5.68 5.52 11 50 5.12 5.64 5.38
Table 4.10 Heating Time in De-ionized water and respective voltage at 100Hz
Sr # Time(Min) Pk-Pk (V) Pk-Pk (V) Avg Pk-Pk 1 0 7.44 7.52 7.48 2 5 4.88 4.96 4.92 3 10 4.96 5.12 5.04 4 15 5.04 5.12 5.08 5 20 5.04 5.44 5.24 6 25 5.52 5.6 5.56 7 30 4.46 5.04 4.75 8 35 4.96 5.12 5.04 9 40 5.2 6.36 5.78 10 45 5.12 5.44 5.28 11 50 5.12 5.84 5.48
Table 4.11 Heating Time in De-ionized water and respective voltage at 150Hz
Sr # Time(Min) Pk-Pk (V) Pk-Pk (V) Avg Pk-Pk 1 0 6.4 6.48 6.44 2 5 4.4 5.28 4.84 3 10 4.8 5.28 5.04 4 15 4.72 4.94 4.83 5 20 5.12 5.2 5.16 6 25 4.96 5.28 5.12 7 30 4.64 5.2 4.92 8 35 4.96 5.2 5.08 9 40 4.64 4.8 4.72 10 45 4.56 4.8 4.68 11 50 4.64 4.8 4.72
69
Table 4.12 Heating Time in De-ionized water and respective voltage at 200Hz
Sr # Time(Min) Pk-Pk (V) Pk-Pk (V) Avg Pk-Pk 1 0 5.28 5.36 5.32 2 5 4.48 4.56 4.52 3 10 4.48 4.64 4.56 4 15 4.32 4.48 4.4 5 20 4.32 4.48 4.4 6 25 4.24 4.4 4.32 7 30 4.48 4.56 4.52 8 35 4.08 4.48 4.28 9 40 4.32 4.56 4.44 10 45 4.32 4.48 4.4 11 50 4.32 4.48 4.4
Table 4.13 Drying time after taking out from de-ionized water at various
frequencies
50Hz 100Hz 150Hz 200Hz Sr # Time
(Min) Avg Pk-Pk Avg Pk-Pk Avg Pk-Pk Avg Pk-Pk 1 0 5.38 5.48 4.75 4.4 2 1 5.32 5.48 5.24 4.68 3 2 5.32 5.48 5.16 4.6 4 3 5.4 6.2 5.42 4.6 5 4 5.4 6.2 4.84 4.84 6 5 5.4 6.2 5.08 5 7 6 5.8 6.4 5.56 5.08 8 7 5.8 6.4 5.88 5.08 9 8 5.8 6.4 5.88 5.08 10 9 6.8 6.4 5.88 5.08 11 10 6.8 6.8 5.96 5.12 12 11 7.2 6.8 5.96 5.12 13 12 7.2 6.8 5.96 5.16 14 13 7.6 6.8 5.96 5.08 15 14 7.96 7.2 5.96 5.08 16 15 7.88 7.2 5.88 5.08 17 16 7.8 7.2 5.88 5.08 18 17 7.76 6.6 5.88 5.08 19 18 7.88 6.6 5.88 5.08 20 19 8.2 6.6 5.8 5.08 21 20 8.2 6.6 5.8 5.08 22 21 8.24 6.8 5.8 5.08 23 22 8.4 6.8 5.64 5.08 24 23 8.48 7 5.96 5.04 25 24 8.52 7 6.2 5
70
26 25 8.52 7.2 6.2 4.96 27 26 8.52 7.2 6.2 4.88 28 27 8.56 7.4 6.2 4.88 29 28 8.6 7.4 6.36 4.84 30 29 8.6 7.48 6.36 5.24 31 30 8.6 7.48 6.36 5.24 32 31 5.24 33 32 5.32 34 33 5.32 35 34 5.32 36 35 5.32
Table 4.14 Heating Time in NaCl solution and respective voltage at 50&100Hz
50Hz 100Hz Time(Min) Pk-Pk (V) Pk-Pk(V) Avg Pk-Pk Pk-Pk (V) Pk-Pk(V) Avg Pk-Pk
0 8.56 8.64 8.6 7.44 7.52 7.48 5 0.32 0.4 0.36 0.32 0.4 0.36 10 0.32 0.4 0.36 0.32 0.4 0.36 15 0.32 0.4 0.36 0.32 0.4 0.36 20 0.32 0.4 0.36 0.32 0.4 0.36 25 0.32 0.4 0.36 0.32 0.4 0.36 30 0.32 0.4 0.36 0.32 0.4 0.36 35 0.32 0.4 0.36 0.32 0.4 0.36 40 0.32 0.4 0.36 0.32 0.4 0.36 45 0.32 0.4 0.36 0.32 0.4 0.36
Table 4.15 Heating Time in NaCl solution and respective voltage at 150&200Hz
150Hz 200Hz Time(Min) Pk-Pk (V) Pk-Pk(V) Avg Pk-Pk Pk-Pk (V) Pk-Pk(V) Avg Pk-Pk
0 6.4 6.48 6.44 5.44 5.52 5.48 5 0.32 0.4 0.36 0.32 0.4 0.36 10 0.32 0.4 0.36 0.32 0.4 0.36 15 0.32 0.4 0.36 0.32 0.4 0.36 20 0.32 0.4 0.36 0.32 0.4 0.36 25 0.32 0.4 0.36 0.32 0.4 0.36 30 0.32 0.4 0.36 0.32 0.4 0.36 35 0.32 0.4 0.36 0.32 0.4 0.36 40 0.32 0.4 0.36 0.32 0.4 0.36 45 0.32 0.4 0.36 0.32 0.4 0.36
71
Table 4.16 Drying Time after taking out from NaCl solution at 50 & 100Hz
50Hz 100Hz Time(Min) Pk-Pk (V) Pk-Pk (V) Avg Pk-Pk Pk-Pk (V) Pk-Pk (V) Avg Pk-Pk
0 0.32 0.4 0.36 0.32 0.4 0.36 1 0.32 0.4 0.36 0.32 0.4 0.36 2 0.4 0.48 0.44 0.32 0.4 0.36 3 0.4 0.48 0.44 0.32 0.4 0.36 4 0.4 0.48 0.44 0.32 0.4 0.36 5 0.4 0.48 0.44 0.32 0.4 0.36 6 0.48 0.48 0.48 0.4 0.48 0.44 7 0.48 0.56 0.52 0.4 0.48 0.44 8 0.48 0.56 0.52 0.4 0.48 0.44 9 0.48 0.56 0.52 0.4 0.48 0.44 10 0.48 0.56 0.52 0.4 0.48 0.44 11 0.48 0.56 0.52 0.4 0.48 0.44 12 0.4 0.48 0.44 0.4 0.48 0.44 13 0.4 0.48 0.44 0.4 0.48 0.44 14 0.4 0.48 0.44 0.4 0.48 0.44 15 0.4 0.48 0.44 0.4 0.48 0.44 16 0.4 0.48 0.44 0.4 0.48 0.44 17 0.4 0.48 0.44 0.4 0.48 0.44 18 0.4 0.48 0.44 0.4 0.48 0.44 19 0.56 0.64 0.6 0.4 0.48 0.44 20 0.56 0.64 0.6 0.4 0.48 0.44 21 0.64 0.72 0.68 0.48 0.56 0.52 22 0.64 0.72 0.68 0.48 0.56 0.52 23 0.72 0.8 0.76 0.48 0.56 0.52 24 1.52 1.6 1.56 0.48 0.56 0.52 25 1.6 1.68 1.64 0.56 0.64 0.6 26 1.68 1.76 1.72 0.8 0.88 0.84 27 1.76 1.84 1.8 0.88 0.96 0.92 28 1.84 1.92 1.88 0.88 0.96 0.92 29 2 2.08 2.04 1.36 1.44 1.4 30 2.08 2.16 2.12 1.44 1.52 1.48 31 2.32 2.4 2.36 1.44 1.52 1.48 32 2.48 2.56 2.52 1.44 1.52 1.48 33 2.96 3.04 3 1.44 1.52 1.48 34 3.28 3.36 3.32 1.52 1.6 1.56 35 3.6 3.68 3.64 1.52 1.6 1.56 36 4.08 4.16 4.12 1.52 1.6 1.56 37 4.4 4.48 4.44 1.52 1.6 1.56 38 4.72 4.88 4.8 1.6 1.68 1.64 39 5.12 5.2 5.16 1.6 1.68 1.64 40 5.44 5.52 5.48 1.6 1.68 1.64 41 5.76 5.84 5.8 1.6 1.68 1.64 42 6.08 6.16 6.12 1.6 1.68 1.64
72
43 6.24 6.32 6.28 1.6 1.68 1.64 44 6.8 6.8 6.8 1.6 1.68 1.64 45 7.04 7.12 7.08 1.68 1.76 1.72 46 7.28 7.36 7.32 1.68 1.76 1.72 47 7.52 7.6 7.56 1.68 1.76 1.72 48 7.68 7.76 7.72 1.68 1.76 1.72 49 7.92 8 7.96 1.68 1.76 1.72 50 7.92 8 7.96 1.76 1.84 1.8 51 8 8.08 8.04 1.76 1.84 1.8 52 8 8.08 8.04 1.76 1.84 1.8 53 8.16 8.24 8.2 1.76 1.84 1.8 54 8.24 8.32 8.28 1.76 1.84 1.8 55 8.24 8.32 8.28 1.76 1.84 1.8 56 8.32 8.4 8.36 1.84 1.92 1.88 57 8.4 8.48 8.44 1.84 1.92 1.88 58 8.4 8.48 8.44 1.92 2 1.96 59 8.48 8.56 8.52 2 2.08 2.04 60 8.56 8.64 8.6 2.16 2.24 2.2 61 2.24 2.32 2.28 62 2.24 2.32 2.28 63 2.4 2.48 2.44 64 2.48 2.56 2.52 65 2.64 2.72 2.68 66 2.72 2.8 2.76 67 2.88 2.96 2.92 68 2.96 3.04 3 69 3.12 3.2 3.16 70 3.2 3.28 3.24 71 3.36 3.44 3.4 72 3.44 3.52 3.48 73 3.52 3.6 3.56 74 3.68 3.76 3.72 75 3.84 3.92 3.88 76 4 4.08 4.04 77 4.16 4.24 4.2 78 4.24 4.32 4.28 79 4.4 4.48 4.44 80 4.48 4.56 4.52 81 4.64 4.72 4.68 82 4.8 4.88 4.84 83 4.88 4.96 4.92 84 4.96 5.04 5 85 5.12 5.2 5.16 86 5.2 5.28 5.24 87 5.28 5.36 5.32 88 5.36 5.44 5.4 89 5.44 5.52 5.48 90 5.52 5.6 5.56 91 5.6 5.68 5.64
73
92 5.68 5.76 5.72 93 5.76 5.84 5.8 94 5.84 5.92 5.88 95 5.92 6 5.96 96 6 6.08 6.04 97 6.08 6.16 6.12 98 6.16 6.24 6.2 99 6.16 6.24 6.2 100 6.24 6.32 6.28 101 6.24 6.32 6.28 102 6.32 6.4 6.36 103 6.4 6.48 6.44 104 6.48 6.56 6.52 105 6.48 6.56 6.52 106 6.48 6.56 6.52 107 6.56 6.64 6.6 108 6.72 6.8 6.76 109 6.88 6.96 6.92 110 6.96 7.04 7 111 7.04 7.12 7.08 112 7.04 7.12 7.08 113 7.2 7.28 7.24 114 7.28 7.36 7.32 115 7.28 7.36 7.32 116 7.36 7.44 7.4 117 7.36 7.44 7.4 118 7.36 7.44 7.4 119 7.44 7.52 7.48 120 7.44 7.52 7.48
Table 4.17 Drying Time after taking out from NaCl solution at 150Hz & 200Hz
150Hz 200Hz Time Pk-Pk (V) Pk-Pk (V) Avg Pk-Pk Pk-Pk (V) Pk-Pk (V) Avg Pk-Pk
0 0.32 0.4 0.36 0.32 0.4 0.36 1 0.32 0.4 0.36 0.32 0.4 0.36 2 0.32 0.4 0.36 0.32 0.4 0.36 3 0.32 0.4 0.36 0.32 0.4 0.36 4 0.32 0.4 0.36 0.32 0.4 0.36 5 0.32 0.4 0.36 0.32 0.4 0.36 6 0.32 0.4 0.36 0.32 0.4 0.36 7 0.32 0.4 0.36 0.32 0.4 0.36 8 0.32 0.4 0.36 0.32 0.4 0.36 9 0.32 0.4 0.36 0.32 0.4 0.36 10 0.32 0.4 0.36 0.32 0.4 0.36 11 0.4 0.48 0.44 0.4 0.48 0.44
74
12 0.4 0.48 0.44 0.4 0.48 0.44 13 0.4 0.48 0.44 0.4 0.48 0.44 14 0.4 0.48 0.44 0.4 0.48 0.44 15 0.4 0.48 0.44 0.56 0.64 0.6 16 0.4 0.48 0.44 0.64 0.72 0.68 17 0.4 0.48 0.44 0.72 0.8 0.76 18 0.4 0.48 0.44 1.2 1.28 1.24 19 0.4 0.48 0.44 2.16 2.24 2.2 20 0.4 0.48 0.44 2.24 2.32 2.28 21 0.48 0.56 0.52 2.4 2.48 2.44 22 0.48 0.56 0.52 2.56 2.64 2.6 23 0.72 0.8 0.76 2.72 2.8 2.76 24 0.8 0.96 0.88 2.88 2.96 2.92 25 0.88 0.96 0.92 2.96 3.04 3 26 0.88 0.96 0.92 3.12 3.2 3.16 27 0.88 0.96 0.92 3.28 3.36 3.32 28 0.88 0.96 0.92 3.44 3.52 3.48 29 0.88 0.96 0.92 3.6 3.68 3.64 30 0.88 0.96 0.92 3.76 3.84 3.8 31 0.96 1.04 1 3.92 4 3.96 32 1.16 1.16 1.16 4.08 4.16 4.12 33 2 2 2 4.16 4.24 4.2 34 2.08 2.16 2.12 4.32 4.4 4.36 35 2.16 2.24 2.2 4.48 4.56 4.52 36 2.24 2.32 2.28 4.56 4.64 4.6 37 2.24 2.32 2.28 4.64 4.72 4.68 38 2.32 2.4 2.36 4.8 4.88 4.84 39 2.48 2.56 2.52 4.88 4.96 4.92 40 2.56 2.64 2.6 4.96 5.04 5 41 2.56 2.64 2.6 5.04 5.12 5.08 42 2.64 2.72 2.68 5.12 5.2 5.16 43 2.72 2.8 2.76 5.12 5.2 5.16 44 2.88 2.96 2.92 5.12 5.2 5.16 45 3.04 3.12 3.08 5.2 5.28 5.24 46 3.12 3.2 3.16 5.2 5.28 5.24 47 3.2 3.28 3.24 5.2 5.28 5.24 48 3.36 3.44 3.4 5.28 5.36 5.32 49 3.44 3.52 3.48 5.28 5.36 5.32 50 3.52 3.6 3.56 5.28 5.36 5.32 51 3.68 3.76 3.72 5.28 5.36 5.32 52 3.76 3.84 3.8 5.28 5.36 5.32 53 3.84 3.92 3.88 5.36 5.44 5.4 54 3.92 4 3.96 5.36 5.44 5.4 55 4.08 4.16 4.12 5.36 5.44 5.4 56 4.16 4.24 4.2 5.36 5.44 5.4 57 4.32 4.4 4.36 5.36 5.44 5.4 58 4.48 4.56 4.52 5.36 5.44 5.4 59 4.64 4.72 4.68 5.44 5.52 5.48
75
60 4.8 4.88 4.84 5.44 5.52 5.48 61 4.88 4.96 4.92 62 4.96 5.04 5 63 5.12 5.2 5.16 64 5.2 5.28 5.24 65 5.28 5.36 5.32 66 5.36 5.44 5.4 67 5.52 5.6 5.56 68 5.6 5.68 5.64 69 5.68 5.76 5.72 70 5.76 5.84 5.8 71 5.84 5.92 5.88 72 5.92 6 5.96 73 5.92 6 5.96 74 6 6.08 6.04 75 6.08 6.16 6.12 76 6.08 6.16 6.12 77 6.08 6.16 6.12 78 6.08 6.16 6.12 79 6.08 6.16 6.12 80 6.08 6.16 6.12 81 6.08 6.16 6.12 82 6.16 6.24 6.2 83 6.16 6.24 6.2 84 6.16 6.24 6.2 85 6.16 6.24 6.2 86 6.16 6.24 6.2 87 6.16 6.24 6.2 88 6.24 6.32 6.28 89 6.24 6.32 6.28 90 6.24 6.32 6.28 91 6.24 6.32 6.28 92 6.24 6.32 6.28 93 6.32 6.4 6.36 94 6.32 6.4 6.36 95 6.32 6.4 6.36 96 6.32 6.4 6.36 97 6.32 6.4 6.36 98 6.32 6.4 6.36 99 6.4 6.48 6.44
100 6.4 6.48 6.44
76
0123456789
0 10 20 30 40 50
Heating Time(Min)
Pk-P
k V
olta
ge(V
)50 Hz
100 HZ
150 Hz
200 Hz
Fig-4.3. Heating time as a function of peak to peak voltage in ordinary water.
0123456789
0 5 10 15 20
Drying Time (Min)
Pk-P
k V
olta
ge (V
)
50 Hz
100 Hz
150 Hz
200 Hz
Fig-4.4 The change in voltage as a function of drying time after immersion in ordinary water.
77
0
2
4
6
8
10
0 20 40 60Heating Time (Min)
Pk-P
k V
olta
ge(V
)
50 Hz
100 Hz
150 Hz
200 Hz
Fig-4.5 Heating time as a function of peak to peak voltage in de-ionized water.
0
2
4
6
8
10
0 10 20 30 40Drying Time (Min)
Pk-P
k Vo
ltage
(V)
50 Hz
100 Hz
150 Hz
200 Hz
Fig-4.6 The change in voltage as a function of drying time after immersion in de-ionized water.
78
0123456789
10
0 10 20 30 40 50Heating time (Min)
Pk-P
k Vo
ltage
(V)
50 Hz
100 Hz
150 Hz
200 Hz
Fig-4.7 Heating time as a function of peak to peak voltage in NaCl solution.
0
1
2
3
4
5
6
7
8
9
10
0 20 40 60 80 100 120 140
Cooling Time (Min)
Pk-P
k V
olta
ge (V
)
50 Hz
100 Hz
150 Hz
200 Hz
Fig-4.8 The change in voltage as a function of drying time after immersion in NaCl solution.
All measurements have been taken at just taken out from water (i.e.. in air). However, if
the peak to peak potential was recorded with the PZT ceramic immersed in water a much
lower value was recorded, for instance 400mV was observed for immersion in ordinary
79
water, in de-ionized water this value was 700mV, and 320mV when dipped in NaCl
solution. Interestingly, when the PZT ceramic was left to stand in air, the peak to peak
potential values returned to their original peaks. The time to return its original value was
about 15 minutes for PZT immersed in water (Fig.4.4) and about 30 minutes for PZT
after immersion in de-ionized water (Fig.4.6). However PZT disc in NaCl solution regain
to its original potential value in one to two hours depending upon the change in frequency
(Fig. 4.8). The difference in drying time between water, de-ionized water and NaCl
solution was attributed to the differences in chemistry of the 3 water conditions. The de-
ionized water lacks ions responsible for dissipating charge from the PZT surfaces, and the
mass effect created by the presence of impurities in the water which will adhere to the
surfaces of the ceramic can affect the peak to peak voltage differences observed between
the solutions.
The properties of PZT ceramics are frequency and temperature dependent. The exact
value for time varied depending on the frequencies used during the test is natural
phenomenon of piezoelectric. As the water particles adhere on the surface after
immersion, reduces the flow of current across the disc and therefore peak-peal voltage
sharply decrease. As long as disc dried, the flow of current increase and after few minutes
it regain its original value when completely dry. The difference in drying time of disc for
water and de-ionized water was attributed to the differences in chemistry between the
different water conditions. The de-ionized water lacks ions responsible for dissipating
charge from the PZT surfaces. The mass effect created by the presence of impurities in
the water which adhere to the surfaces of the ceramic can affect the peak to peak voltage
differences observed between the solutions. The lack of ions in de-ionized water may
80
increase the resistance and hence drop in voltage is less as compared to ordinary water.
The most noticeable behavior was seen when the PZT ceramic was immersed in a
solution of NaCl as shown in Fig.4.7 and Fig.4.8. A significant decrease in potential was
observed for the PZT ceramic with values dropping to 320mV after the immersion tests.
When the PZT ceramic was allowed to dry in air the disc took a longer time to regain its
original potential value depending on the frequency used during the test. This is because
of the crystalline nature of NaCl, its particles adhere to the surface and took a longer time
to evaporate and hence to regain its original output value in long time. These results
clearly showed that the PZT ceramic is sensitive to the type of solution in contact with
the ceramic surface. Earlier W.P.Chen [68] observed the degradation phenomenon in
PZT ring for determination of its various piezoelectric properties in NaOH solution by
electrolysis of water and by high power resonant driving. In their study degradation in
capacitance, dielectric loss, impedance and Pk-Pk voltage change with respect to time
and frequency have been examined. In contrast to these above stated properties, the
present work has been conducted to measure the performance characteristics of PZT disc
in water and NaCl solution in heating cycle with respect to time at variable frequencies.
Previous findings [66, 68] clearly state that the change in temperature changes the out put
peak to peak voltage and other piezoelectric properties of PZT. The work conducted by
Jiang [71] concluded that piezoelectric devices seriously degrade by hydrogen in water
due to electricity. Atomic hydrogen formed by electrolysis of water degrades dielectric
and mechanical quality factor with respect to hydrogen charging time. The present work
has an agreement with their finding in changing the Pk-Pk voltage with time at variable
frequencies. Influence of hydrogen charging on the current-voltage characteristics of a
81
PZT ring measured by Jiang [71] resulted in the form of decrease in resistivity of the
sample. This decrease in resistivity is due to the reduction reaction of atomic hydrogen
resulting in the formation of charge carriers in piezoelectric ceramics material. In figures
4.3, 4.5 &4.7, it is clear that the drop in voltage occurs, which is due to decrease in
resistance across the disc and a well documented phenomenon as discussed by earlier
researchers. Another parameter observed in the current research work is the ability of
material to retain the original potentials.
Effect of heating rate on dielectric and pyroelectric properties of PZT have been reported
by Mohiddon [73] and founded that heating rate influence the capacitance and dielectric
properties. Increasing heating rate reduces the level of evaporation. In present work a
qualitative data obtained during the drying cycle of PZT disc after immersion test till the
complete evaporation. Here the test was conducted at constant heating and cooling rate
but a change in peak-peak voltage has also been observed and shown in figures 4.4, 4.6
&4.8. This change in potential is attributed to the change of medium and frequency.
Therefore there is a scope of further research to conduct the same experimentation at
different heating and cooling rate to observe the performance characteristics of thin PZT
in various environmental conditions.
82
4.3 Phase-2 Thermal cycling/shocking of thin PZT disc
Earlier fatigue studies showed that materials degrade due to change in
environmental temperatures. Thermal shocking is one of the most severe phenomenons in
degradation of piezoelectric ceramics. A lead zirconate titanate thin piezoelectric disc has
been analyzed to observe its thermal cycling/shocking effect.
4.3.1 Specimen
A Lead Zirconate Titanate piezoelectric disc 0.191mm thick and 12.7mm
diameter supplied by Piezo System Inc. used for the experimentation. The specimen was
nickel electroded on major faces and its dielectric constant was about 1850 @1KHz,
Curie temperature 3500C, and density 7800 Kg/m3. In this case the specimen was not
soldered and was used as in its as received form.
4.3.2 Instrumentation
The instrumentation used in this case has also been described in chapter-3. Thin
PZT disc was placed on a small metallic strip and a spring loaded thermocouple was
directly attached on upper surface of the disc. Thermocouple attached with data
acquisition system which indicate the temperature of the specimen. A stop watch used to
measure the time to reach at specific temperature.
4.3.3 Testing/Measurements
Following experimentations were done at different condition to analyze the
degradation in piezoelectric properties. All testing were done well below the curie
temperature of the piezoelectric specimen.
83
1. Thermal shocking from 1000C from thermal chamber to de-ionized water at 200C.
2. Thermal cycling test between 1000C and 900C for 60 cycles in step of 10 cycles.
3 Shocked once for 60Cycles between 1000C and 900C
4 Thermal shocking from 1500C & 1000C from thermal chamber to de-ionized
water at 200C.
4.4 Thermal shocking from 1000C from thermal chamber to de-ionized
water at 200C.
A lead zirconate titanate thin piezoelectric disc has been analyzed to observe its thermal
shocking effect. Disc was shocked from 1000C from a thermal chamber environment to
de-ionized water at 200C. Dielectric constant, impedance and coupling factors at
frequency of maximum and minimum impedance have been measured for thirty five
shocks. The change in dielectric constant, Impedance and other piezoelectric parameters
were observed by using relevant instrumentations. The change in degradation will be
very useful in modeling and development of sensitive piezoelectric instruments.
Lead Zirconate Titanate (PZT), Barium Titanate (BaT1O3), and Lead Metaniobate
(PbNb2O6) are smart sensing materials. These materials are being used in critical
engineering systems and smart structures. Piezoelectric materials when undergoes a
cyclic stress during thermal environment may degrade the piezoelectric properties [76].
Heat transfer effect in ferro-electric materials, electric impact loading, thermal effects of
piezoelectric sensors and heat generation rate in piezoelectric materials have also been
investigated by various researchers [77]. Thermal shocks in a plate of finite thickness
have been attempted. Thermal shock and thermal fatigue of ferroelectric thin film were
84
investigated by the pulsed laser tests by X.J.Zheng et. al [67]. Fatigue studies show that
material degradation of PZT ceramics are strongly influenced by temperature and by the
electromechanical fatigue. Lead zirconate titanate ceramics shows a decrease in dielectric
constant and the resonance frequency when subjected to thermal shock. Importance of
temperature stability for dielectric constants and resonance frequencies have been
discussed [78]. Thermal shock resistance of the materials was evaluated by water
quenching and a subsequent three point bending test to determine flexure strength
degradation. Degradation of various properties of the piezo devices in the presence of
water & AC voltage was investigated and concluded that water is an important cause for
the degradation of PZT piezoelectric ceramics [72].
Dielectric constant is an important parameter, especially in the piezoelectric device such
as resonators and filters used in the electronic circuits. Impedance is also dependent on the
dielectric constant of the piezoelectric. Currently there is limited data available for the
thermal shocking and quenching effect of a thin PZT disc. In this part of research work,
the focus was to investigate the degradation of thin PZT disc due to thermal shocking and
its quenching effect in de-ionized water. A noticeable change in capacitance and
dielectric constant has been observed which is further changing other piezoelectric
properties. Current research part is a unique finding in thermal shocking and quenching
of thin PZT disc.
85
4.4.1 Test Setup and Variables.
There is no single technique for measuring piezoelectric material characteristics.
However some standards allow measuring some parameters and then using the
appropriate relationships, other piezoelectric parameters can be found.
A piezoelectric thin PZT disc has been investigated under thermal shocking in de ionized
water. Initially the capacitance, dissipation factor, impedance, and phase angle of the as
received specimen have been measured. For the reliability of results two discs have been
used at same time for the shocking and measurements in the same environmental
condition. Rate of change in temperature in thin PZT disc in thermal chamber from 200C
to 1000C and after removing from thermal chamber shocked in de ionized water at 200C
has been clearly shown in Fig.4.9. Disc heated in thermal chamber at rate of
10.860C/min.
0
20
40
60
80
100
120
0 2 4 6 8 10
Time in Minutes
Tem
pera
ture
in C
Fig.4.9 Rate of change in temperature from 200C to 1000C from thermal chamber and shocking at 200C in de-ionized water
86
The specimen was placed in an environmental chamber and heated to 1000C and then
suddenly removed and quenched in de-ionized water at about 200C for a specific time and
then dried. The specimen was again placed in the thermal chamber for the same
temperature range and quenched again. Five such shocks were introduced. The values of
capacitance and impedance after these five shocks were measured at a frequency of
1KHz. and at fm & fn. Six series each with five shocks have been performed and their
respective capacitance and impedance values have been measured. Data collected for
thirty five such shocks and analyzed for the degradation in dielectric constant and
coupling factor. Frequencies of maximum and minimum impedance were observed
between 100 KHz and 200KHz. Capacitance and Impedance at theses particular
frequencies were recorded. The values of capacitance were used to calculate the dielectric
constant by using equation-4.1.
Effective and Transverse coupling factors has been determined by using the relationships
4.2 and 4.3
Where Ψ = π/2(fn/fm) * tan |π/2 * (fn-fm)/fm|
30
ta x CpK T
A x =
∈
Keff =
K31 = SQRT (ψ/(1+ψ)
(4.1)
SQRT (fn2 – fm
2)/fn2
(4.2)
(4.3)
87
Capacitance and impedance of the tested specimen were measured by using impedance
analyzer and dielectric text fixture. Dielectric test fixture model 16451B was selected as
fixture for the testing material. The fixture was attached with LCR meter and impedance
analyzer 4294A which use the 4-terminal pair measurement configuration. Electrode-D
of the test fixture was selected for measurements. This electrode is appropriate to
measure those materials which already have thin film electrodes. The values obtained
from impedance analyzer then used for the calculation of dielectric constant, and
coupling factors (Keff, and K31). Table-4.18 indicates the values obtained and used for
the calculation of above mentioned parameters according to the IEEE standard [53].
Table-4.18 Values of Capacitance Coupling factors and dielectric constant w.r.t.
frequency of maximum (fm) and frequency of minimum (fn) impedance.
fm fn Cpat1KHz Cp atfm Cp at fn Keff K31 K3
T at fm Shock# Hz Hz pF pF pF
0 160000 165500 10880 58040 -52967 0.255 0.279 9888 5 156785 165106 11100 55650 -53045 0.313 0.34 9481 10 151570 160270 11220 45350 -36430 0.324 0.352 7726 15 147075 154530 11330 37520 -22150 0.306 0.333 6392 20 142000 152500 11260 31060 -16741 0.364 0.393 5291 25 141000 156000 11280 28120 -11570 0.427 0.457 4790 30 123000 157000 11320 20250 -1140 0.621 0.644 3450 35 116500 153500 11320 17230 250.35 0.651 0.671 2935
Impedance analyzer and test fixture is shown in figure 4.10.
88
Fig. 4.10 Impedance analyzer connected with test fixture for measuring various parameters (Impedance, Capacitance, Dissipation factor, Phase angle).
4.4.2 RESULTS ANALYSIS
The measurement of capacitance and dielectric constant during thermal shocking was
done by precise instrumentation. The latest impedance analyzers and compatible test
fixtures have the capability to measure these parameters accurately. The dielectric
constant and coupling factor were measured as a function of frequency of maximum
impedance and frequency of minimum impedance. Thin disc shocked in de-ionized water
shows a noticeable difference between shocked and unshocked condition at frequency of
maximum impedance and at frequency of minimum impedance. This difference has been
thought to be attributed due to change in dipole movement and direction. Affect on grain
size if any is not considered in this study as beyond the scope of preset work. Shocked
Materials capacitance values measured before testing and after every five shocks. Fig-
4.11 (a&b) indicate the capacitance values at frequency of maximum and minimum
89
impedance before conduction of test for which only one peak has been observed , where
as the number of peaks have been observed for the shocked material at frequency of
maximum and minimum impedance and clearly indicated in Fig-4.12(a&b). Dissipation
factor is also greatly affected by thermal shocking conditions as indicated in Fig 4.11&
4.12. With the measurements conducted after every five shocks, values for maximum and
minimum impedance has been observed at different frequencies. The value of
capacitance at frequency of maximum and minimum impedance shows very interesting
results. The detailed experimental results images have been presented in Appendix-A
90
(a)
(b)
Fig-4.11 Value of capacitance for Un-shocked Disc (a). Capacitance at frequency of
maximum impedance. (b). Capacitance at frequency of minimum impedance.
91
(a)
(b)
Fig-4.12 Value of capacitance after thirty five shocks
(a). Capacitance at frequency of maximum impedance
(b). Capacitance at frequency of minimum impedance
92
-10000
-5000
0
5000
10000
15000
0 10 20 30 40
Number of shocks
Die
lect
ric c
onst
ant i
n pF
At 1KHz
fm 100C
fn 100C
Fig-4.13 Change in Dielectric constant w.r.t. Number of shocks
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 10 20 30 40Number of shocks
Cou
plin
g fa
ctor
Keff
K31
Fig-4.14 Coupling Factors with respect to Number of Shocks
93
Frequency of maximum impedance observed for unshocked specimen was 160 KHz,
where as after thirty five shocks it was about 116.5 KHz which is approximately 28
percent less from the unshocked value. Similarly frequency of minimum impedance
observed at 165.5 KHz for unshocked and 153.5 KHz for socked specimen which is only
7.5 percent less from unshocked specimen value. This difference shows that the
maximum and minimum resonance is dependent on their respective frequencies. It is
observed that value of capacitance continuously going to decrease from initial to shock
condition at frequency of maximum impedance and reverse at frequency of minimum
impedance. By using equation-4.1 dielectric constant calculated with respect to number
of shocks and indicated in Fig.4.13. Dielectric constant is very important property and
depends upon the physical condition of the material. The change in dielectric constant in
this work clearly indicates that physical condition of the material has been changed due to
change in dipole lengths and directions. The change in capacitance and the relative
dielectric constant is due to dipole moments inside the material. Due to thermal shocks,
the displacement of electrons may cause re-orientation of these dipoles. The
misalignment of polarization and displacement of charge may result in random
orientation of the dipoles, which further changes its capacitance and dielectric values.
The description of dielectric constant is very difficult in thermal cycling problems
because the orientations of molecular size dipoles changes frequently in such shocking
conditions. Theory becomes more difficult because of electrostatic interaction between
dipoles. However, the measurement of fm and fn is one of the reliable methods to
determine the capacitance value at particular frequency. The relative difference in the
frequencies of maximum and minimum impedance depends on both the material coupling
94
factor and resonator geometry. For this reason a quantity called the effective coupling
factor has been used. Effective and transverse excitation coupling factor has been plotted
by using equation-4.2 & 4.3 and indicated in Fig.4.14. Earlier the stress dependence of
electromechanical properties of various piezoelectric ceramics has been reported.
Viehland [79] found that coupling coefficients and piezoelectric coefficients are
relatively high under stress. He determined the effect of uniaxial stress upon the
electromechanical properties of various piezoelectric ceramics. The change in values was
observed with the change in stress and electric field. In the present work, effective and
transverse excitation coupling factors have been determined by resonance method. After
thermal shocking, the transverse and effective coupling factors increased and became
very close to each other. The decrease in fm was accompanied by decrease in fn and their
difference was continuously increasing with thermal shocking. This difference resulted in
the increase in coupling factor. A thermal stress developed in the thin PZT due the
thermal shock that may have caused an increase in the coupling factor. It was observed
during the experimentation that wrong selection of guarded electrode and the distance of
PZT disc from the edges under the guarded electrode may affect the results. Therefore,
for the reliability of the results, the values were taken with absolute care in placing the
specimen under the electrode, and were repeated for shocking and measurements.
Trend for both coupling factors is in increasing order and show very close agreement to
each other.
95
4.5 Phase-2 (Series 2) Thermal shocking from 1500C & 1000C from
thermal chamber to de- ionized water at 200C.
Earlier thermal shocks in a plate of finite thickness have been attempted. Fatigue studies
show that material degradation of PZT ceramics are strongly influenced by temperature.
Lead zirconate titanate ceramics shows a decrease in dielectric constant and the resonance
frequency when subjected to thermal shock. In many piezoelectric applications, materials
with high dielectric constant and high electromechanical factor are required. It has been
reported that dielectric constant increases with heating rate increase [80].Other studies
reported that increasing heating rate may affect the evaporation and optimum dielectric
constant found at certain specific value [81]. Thermal fatigue test method include the
quench method and repeated heating method has been for thermal shocks and discussed
earlier by Lamon and Pherson (1981, 1991) [82, 83].Therefore there was a scope to
investigate these important behaviors of the materials during different thermal shocking
temperatures. Water is an important cause of degradation of a PZT ceramics. The
experimental results obtained have been compared between both shocking conditions and
the sensitivity between two shocking ranges has been observed.
4.5.1 EXPERIMENTATION
Sudden heating and cooling of piezoelectric ceramics material may cause high
value of stresses and therefore change in internal properties of the material may occur. In
this series thin lead zirconate titanate discs have been investigated during thermal
shocking in de-ionized water from 1000C to 200C and from 1500C to 200C.
96
Experimentation was performed for thirty five shocks and their relative dielectric
constant, coupling factor and impedance have been measured. A Lead Zirconate Titanate
piezoelectric disc nickel electroded on major faces, 0.19mm thick and 12.7mm in
diameter was used for the experimentation. Thin piezoelectric ceramic discs were heated
using a heating rate of 9oC/min up to 100oC, and 1500C using a thermal chamber and then
quenched in de-ionized water at a temperature 20oC. For all thermal cycling and
quenching experiments 2 PZT test samples were used and subjected to identical
conditions in order to confirm reliability. The temperature of the PZT samples were
measured using a spring loaded thermocouple and data acquisition system attached
directly to the samples. In order to observe degradation phenomenon of the PZT ceramic,
the capacitance, dissipation factor and impedance were measured at a frequency of 1 KHz
at the start and after every 5 heating and quenching cycles. Data was collected for a total
of 35 thermal cycles. All described parameters were also measured at frequencies of
maximum and minimum impedance by using impedance analyzer. By considering
various frequency ranges, the frequency of maximum and minimum impedance was
observed between 100 KHz and 200 KHz Change in dielectric constant, coupling factor
and impedance for thirty five shocks in de-ionized water has been tabulated in Table-
4.19. The recorded values are at 1 KHz and at a frequency of maximum impedance.
97
Table-4.19 Change in Dielectric Constant and Coupling Factor for two Different Thermal Shocking Conditions. Shocking from 1000C to 200C Shocking from 1500C to 200C
Shock# TK 3
at 1KHz
TK 3 at fm effK 31K
TK 3 at 1KHz
TK 3 at fm effK 31K
0 1853 9888 0.255 0.279 1869 10462 0.23 0.26 5 1891 9481 0.313 0.34 1915 8532 0.27 0.29
10 1911 7726 0.324 0.352 1923 7005 0.3 0.32 15 1930 6392 0.306 0.333 1932 4366 0.32 0.35 20 1918 5291 0.364 0.393 1954 3926 0.34 0.37 25 1922 4790 0.427 0.457 1976 3504 0.36 0.38 30 1928 3450 0.621 0.644 1976 3912 0.41 0.41 35 1928 2935 0.651 0.671 1976 4121 0.44 0.47
4.5.2 RESULT ANALYSIS
The changes in dielectric constant and coupling factor were measured as a
function of fm and fn. It is observed that an increase in the value for the capacitance of the
as-received PZT ceramic was 5.8 x 104 pF and this value gradually decreased with
increasing thermal cycling (1000C-200C)to 1.72 x 104 pF. A corresponding change in the
fm was observed with a value of 160 KHz for the PZT sample at the start and then the
value decreased to 116.5 KHz. This represented a 28% decrease in the fm after the
ceramic was thermally cycled. A similar change was observed for the fn which decreased
from 165.5 KHz for the as-received to 153.3 KHz after 35 thermal cycles. For the thermal
cycling (1500C-200C) change in fm observed from 160.2 KHz to 141 KHz and this change
is from 165.175 KHz to 157.5 KHz at fn.
A comparison of the graphical output for dielectric constant for the PZT samples before
thermal cycling and then after exposing the ceramic to 35 heating and quenching cycles is
shown in Fig.4.15. Dielectric constant remains independent when measured at 1 KHz.
The dielectric constant is an intrinsic property of the ceramic material and the results
98
show that this value decreases with increasing thermal cycles at fm and vice versa. The
relative difference in the frequencies of the maximum and minimum impedance values
depends on the material coupling factor and the resonator geometry (i.e.. dimensions of
the ceramic PZT sample). For this reason a quantity known as the effective coupling
factor (Keff) and the transverse excitation factor (K31) calculated and were compared as a
function of the number of thermal cycles, see Fig.4.16. The results show that both
temperature difference values for K31 and Keff increase with increasing thermal cycles to
which the PZT ceramic is exposed.
Figure 4.15. Chang in dielectric constant against number of shocks, at frequency
1 KHz, at frequency of maximum impedance, at frequency of minimum impedance.
-15000
-10000
-5000
0
5000
10000
15000
0 10 20 30 40
Die
lectr
ic c
on
sta
nt in
pF
Number of shocks
Shocking from 100 0C – 20 0C at 1KHZ.
100 0C – 20 0 C at fm.
100 0C – 20 0 C at fn. 150 0C – 20 0 C at 1KHz.
150 0C – 20 0 C at fm.
150 0C – 20 0 C at fn.
99
Shocked from
100 0C - 20 0C at fm.
100 0C - 20 0C at fn.
150 0C - 20 0C at fm.
150 0C - 20 0C at fn.
Figure 4.16. Change in coupling factor (K31, Keff) against number of shocks from
100 0C – 20 0C & from 150 0C – 20 0C in de-ionized water.
0
20
40
60
80
100
120
140
160
0 10 20 30 40Number of Cycles
Mod
ulus
of I
mpe
danc
e in
O
hms
Figure 4.17. Change in Modulus of impedance ( |Z| ) against number of shocks from
100 0C – 20 0C & from 150 0C – 20 0C in de-ionized water.
The change in Modulus of Impedance for two different shocking conditions has been
evaluated and is shown in fig.4.17. The Modulus of impedance both for fm and fn when
shocked from 1000C to 200C, going to increase where as for the other condition it starts
decreasing after twenty five shocks.
Resonance and anti resonance frequencies are the measure of electromechanical coupling
factor. The coupling between the electrical excitation and mechanical vibration determine
Shocked from
Keff, 100 0C - 20 0C
K31, 100 0C - 20 0C
Keff, 150 0C - 20 0C
K31, 150 0C - 20 0C0
0.2
0.4
0.6
0.8
0 10 20 30 40Number of shocks
Cou
plin
g fa
ctor
100
its piezoelectric effect. Mechanical vibrations appears like a series LCR circuit to the ac
source. Such circuits have minimum impedance at certain frequency called resonance
frequency (fn). There is another frequency at the other end and is called anti-resonance
frequency (fm). The change in electromechanical coupling factor changes the out put
performance and characteristics of the piezoelectric material by thermal shocking.
The comprehensive results with images have been presented in Appendix-A.
101
4.6 .Phase-3 (Series 3) Effect of Frequency and Resistance on Pk-Pk
Voltage with respect to Temperature Change
This phase describes the experimentations performed on thin PZT disc for the
determination of its thermal cycling behavior at a specific temperature ranges and at
different frequencies and resistances. The aim was to determine the output voltage across
the specimen at different variables. A mathematical model has been developed for the
specific temperature range at various frequencies to determine the peak-peak voltage and
to demonstrate the effect of frequency with respect to change in resistance. Sensitivity
due to temperature, resistance and frequency was observed. The data recorded and
analyzed will be very useful in selecting the particular range for the output performance
needed for the fabrication of any specific piezoelectric instrumentation. The aim of this
part of work was to analyze the sensitivity of the thin PZT disc in thermal environment.
Lead zirconate titanate (PZT) ceramics materials are widely used in various applications
like in micro sensors, actuators, resonators, vibrators, etc. The functioning of these smart
materials is very much depended on various conditions such as change in frequency,
resistance and temperature etc. These variables may affect the output performance of the
instrument in which they used and therefore considered highly sensitive.
Reliability of instruments is very important and research has been carried out on PZT and
BatiO3 (Barium titanate) thin films. Piezoelectric coefficients are temperature dependent
in PZT film and this temperature change may expect in variation of output signals. A
frequency response measurement has been used to measure the sensitivity of
piezoelectric devices [84]. Piezoelectric have been investigated for their thermoelectric
102
behaviors and various governing equations for thermal affects has been described [85].
P.K. Panda et. al. in their investigation analyzed that thermal stresses is sensitive to
thickness of samples and, therefore, they recommended using various samples of same
thickness to get the reliable results [86]. Thermal fatigue methods including quenching
[87] and repeative heating method have been described earlier [88].
Piezoelectric ceramics under electric fields becomes non linear due to domain effects.
Effect of power on the rise of temperature of piezoelectric materials is also an observed
phenomenon. In this research work effect of temperature on thin PZT discs have been
investigated with respect to change in frequency and resistance for the functional
performance in the form of peak to peak voltage. The aim was to determine how these
parameters influence the characteristics of PZT disc at room temperature (200C) and at a
temperature 1600C well below the curie temperature of PZT specimen.
4.6.1 Experimental Setup
Figure-4.18 shows the arrangement for the experimental setup including thermal
chamber, temperature recording system, decade resistor, function generator, oscilloscope
and thermocouple. A schematic diagram of the experimental arrangement showing the
circuitry connections has been described in Fig-4.19
103
Fig-4.18 Experimental arrangement for the determination of out put Peak-Peak voltage
104
Figure 4.19 Schematic Arrangement of Thermal Cycling Circuitry
105
4.6.2 Experimentation
A soldered specimen attached with the described circuitry as shown in Fig-4.19
was mounted in the thermal chamber environment. The measurements were taken at
various temperatures ranges. A WaveTek Model FG-273 function signal generator of
kenwood was used for the excitation of piezo disc at various frequencies. Frequencies
selected were 50, 100, 150, 200, and 300 Hz. Resistances were selected by a decade
resistor type 1434-G of General Radio Company. The range of the decade resistor is 0 to
b1000 KΩ. Out put voltages were obtained by Tektronix TDS 210 oscilloscope. The
voltage across Channel-1 and Channel-2 of the oscilloscope were kept constant at 5V and
2V respectively. The description of the specimen and it properties has been described in
chapter 3. Nickel electroded specimen (Fig.4.20) was soldered and attached with
thermocouple which determines the surrounding temperature of the specimen. Series-1 of
the experiment was performed at room temperature and Series-2 at 160 0C. For the
reliability/validity of results the experimentation was repeated with same specifications
and with same environmental conditions in each Series.
106
Fig-4.20 Piezoelectric PZT disc (diameter 12.7mm and thickness 0.191mm)
4.6.3 Series-1(At Room Temperature)
In this series of experimentation, all measurements were taken at room
temperature. Room temperature was about 200C with a temperature vitiation of ± 20C.
The specimen was attached with the designed circuitry and measurements were taken at
50, 100, 150,200 and 300 Hz. Experimental setup for this series of experimentation is
shown in figure 4.21. The out put Pk-Pk voltage were recorded against resistances. Data
obtained has been recorded and noted in Table-4.20. The value obtained at 0k ohm was
always 10.2 Volt, i.e.. the maximum voltage across the piezo disc without resistance.
This value starts decreasing with the increase in resistance. Figure 4.22 shows the
behavior of voltage drop with respect to increase in resistance. Voltage drops
continuously with the change in resistance, but this decrease is also a frequency
dependent. At the higher values of frequencies the drop in voltage is higher.
107
Fig-4.21 Experimental arrangement for the determination of output voltage at room temperature (200C).
Table-4.20 Change in Pk-Pk Voltage against Resistances at 200C (RT)*
Frequency(Hz) 50Hz 100Hz 150Hz 200Hz 300Hz Resistance(KΩ) Pk-Pk(V) Pk-Pk(V) Pk-Pk(V) Pk-Pk(V) Pk-Pk(V)
0 10.2 10.2 10.2 10.2 10.2 1 10.2 10.2 10.2 10.2 10.2 10 10.1 10.1 10.1 10.1 9.92 20 9.92 10 9.76 9.68 9.28 30 9.84 9.76 9.36 9.2 8.48 40 9.68 9.52 8.96 8.56 7.68 50 9.52 9.28 8.56 8.16 6.96 60 9.44 8.96 8.16 7.6 6.32 70 9.28 8.72 7.76 7.12 5.68 80 9.12 8.4 7.36 6.64 5.28 90 8.96 8.16 6.96 6.24 4.88 100 8.8 7.84 6.56 5.84 4.48 110 8.4 7.36 6.24 5.36 4 200 7.28 5.6 4.16 3.52 2.56 300 6.08 4.24 3.12 2.48 1.84 400 5.12 3.44 2.32 2 1.44 500 4.48 2.88 1.92 1.68 1.2 600 3.92 2.48 1.68 1.44 1.04 700 3.44 2.24 1.52 1.28 0.96 800 3.12 2 1.36 1.2 0.88 900 2.88 1.84 1.2 1.12 0.88
1000 2.72 1.68 1.12 1.04 0.88
108
0
2
4
6
8
10
12
0 200 400 600 800 1000 1200Resistance in K Ohms
Pk-P
k Vo
ltage
(V)
50 HzRT
100HzRT
150HzRT
200 HzRT
300 HzRT
Figure-4.22 Effect of resistance on Pk-Pk voltage at various frequencies at room temperature.
This drop in voltage is high at higher frequency as compared to low frequency. Output
voltage is greatly affected with the resistance. For example, at frequency 50 Hz &
resistance 10 KΩ, the Pk-Pk voltage is 10.1V and at the same resistance, the value at
300Hz is 9.92Volt i.e.. difference in voltage is only 0.18V. The difference is increased to
4.32V at 100 KΩ and further this difference reduces to 1.92V at 1000KΩ. It is also
observed that drop in voltage is very much dependent on frequency. For example at
frequency 50 Hz, the drop in voltage from 10 KΩ to 100KΩ is from 10.1V to 8.8V i.e..
(1.3V), whereas for the same range of resistance and at 300 Hz this value changes from
9.92V to 4.48V i.e.. (5.44). Interestingly this behavior changes from 100KΩ to 1000KΩ.
For this range the drop in voltage at 50Hz is 6.08V and 3.68V at 300Hz. This behavior is
clearly indicated in figure-4.22, that at 50 Hz the drop in voltage from 0-100kΩ is less
and this drop is more from 100-1000KΩ. This phenomenon is reversed at 300Hz which
shows that the maximum drop is from 0-100 KΩ and less decrease for the higher value of
109
resistance. In conclusion it is determined that drop in voltage in piezoelectric disc is very
much dependent on resistance and frequency even at room temperature. The sensitivity
observed will be very useful for the designing of piezoelectric systems for particular
applications.
Table 4.21 indicates the difference in voltage for each hundred resistance band for each
frequency. Fig 4.23 indicates the change in voltage between each 100 K ohms band.
Table 4.21 Difference in voltage for each 100kΩ band at room temperature (200C)
Frequency(Hz) 50Hz 100Hz 150Hz 200Hz 300Hz Resistance(KΩ) Pk-Pk(∆V) Pk-Pk(∆V) Pk-Pk(∆V) Pk-Pk(∆V) Pk-Pk(∆V)
1-100 1.4 2.36 3.64 4.36 5.72 100-200 1.52 2.24 2.4 2.32 1.92 200-300 1.2 1.36 1.04 1.04 0.72 300-400 0.96 0.8 0.8 0.48 0.4 400-500 0.64 0.56 0.4 0.32 0.24 500-600 0.56 0.4 0.24 0.24 0.16 600-700 0.48 0.24 0.16 0.16 0.08 700-800 0.32 0.24 0.16 0.08 0.08 800-900 0.24 0.16 0.16 0.08 0 900-1000 0.16 0.16 0.08 0.08 0
110
0
1
2
3
4
5
6
7
1 2 3 4 5 6 7 8 9 10
Resistance band
Pk-P
k Vo
ltage
(V)
50 Hz100Hz150Hz200Hz300Hz
Figure 4.23 Change in Pk-Pk voltage for each 100kΩ band at 200C
Table-4.22 indicates the resistance ranges i.e.. for each 100 kΩ resistance
band.
Table 4.22 Resistance Range Bands
Band No. Resistance range in kΩ 1 1 - 100 2 100 - 200 3 200 - 300 4 300 - 400 5 400 - 500 6 500 - 600 7 600 - 700 8 700 - 800 9 800 - 900 10 900 - 1000
111
4.6.4 Series -2 (At 1600C)
Piezoelectric disc was analyzed to observe the effect of temperature at variable
resistances. The same disc was mounted in a thermal chamber and its temperature peak
was selected at 1600C. At this temperature Pk-Pk voltage was recorded with respect to
resistance and frequency. All measurements were taken at surrounding environmental
temperature 1600C. The behavior of output voltage was observed by keeping the
reference temperature constant for few minutes. It was observed that there was no effect
of time at this specific temperature. The change in values was observed by changing the
frequencies and resistances are tabulated in table.4.23. Figure-4.24 indicates the behavior
of thin PZT disc for this specific condition. The out put voltage recorded at 50, 100, 150,
200 and 300 Hz frequencies. Overall drop in voltage was more as compared to previous
case at room temperature. For example at this temperature, the Pk-Pk voltage from 10KΩ
-1000KΩ and at 50 Hz changes from 10V to 2V. At room temperature with the same
conditions the drop in voltage was 10.1V to 2.72V. This indicates that temperature is
definitely affecting the output response of PZT disc. At high temperature the drop in
voltage from lower to high value of resistance is high.
There was no change in output voltage at various frequencies at 0 K ohm resistances.
The value of Pk-Pk voltage stared decreasing from 10 K Ω to 1000 K Ω. A threshold
value was 10 K Ω where from the values stars changing. The value for output voltage
obtained at 50 Hz and at 10 K Ω was 10 volts. This value decreases to 2 volts at 1000K
Ω, i.e.. 80% decrease. The decrease in the value was not independent of frequency and
this value continuously decreases with different percentage. At 300 Hz the value at 10 K
Ω was 9.6 volt, and it decreases to 0.64 volt i.e.. 93.33% decrease from 10 k Ω value.
112
This means that voltage drop at low frequency is less as compared to voltage drop at high
frequency. Another interesting behavior was relating to change in Pk-Pk voltage by
changing the resistance value. It is clear in Figure-4.24 that drop in voltage is also
dependent on frequency input and resistances. This drop in voltage is less at low
frequencies, whereas at high value of frequency the output voltage drop is high enough.
Table-4.23 Change in Pk-Pk Voltage with respect to Resistances at 1600C
Frequency(Hz) 50Hz 100Hz 150Hz 200Hz 300Hz Resistance(KΩ) Pk-Pk(V) Pk-Pk(V) Pk-Pk(V) Pk-Pk(V) Pk-Pk(V) 0 10.2 10.2 10.2 10.2 10.2 1 10.2 10.2 10.2 10.2 10.2 10 10 9.92 9.92 9.84 9.6 20 9.84 9.76 9.6 9.2 8.56 30 9.68 9.44 9.04 8.48 7.44 40 9.44 9.12 8.48 7.76 6.48 50 9.36 8.72 8 7.04 5.6 60 9.12 8.32 7.36 6.4 4.96 70 8.88 7.92 6.88 5.84 4.4 80 8.72 7.52 6.4 5.36 4 90 8.56 7.2 6 4.96 3.6 100 8.32 6.8 5.6 4.64 3.36 110 8.08 6.56 5.28 4.4 3.2 200 6.48 4.48 3.36 2.64 1.84 300 5.12 3.28 2.4 1.92 1.36 400 4.16 2.56 1.84 1.52 1.04 500 3.52 2.16 1.6 1.2 0.96 600 3.12 1.84 1.36 1.12 0.8 700 2.72 1.68 1.2 1.04 0.72 800 2.4 1.52 1.04 0.96 0.72 900 2.24 1.36 0.96 0.8 0.72 1000 2 1.28 0.96 0.72 0.64
113
0
2
4
6
8
10
12
0 200 400 600 800 1000 1200
Resistance in K Ohms
Pk-P
k Vo
ltage
(V)
50 HzHT
100 HzHT
150 HzHT
200 HzHT
300 HzHT
Figure-4.24 Effect of resistance at Pk-Pk voltage at various frequencies and at temperature 1600C
Table-4.24: Difference in voltage for each 100kΩ band at 1600C
Frequency(Hz) 50Hz 100Hz 150Hz 200Hz 300Hz Resistance(kΩ) Pk-Pk(∆V) Pk-Pk(∆V) Pk-Pk(∆V) Pk-Pk(∆V) Pk-Pk(∆V) 1-100 1.88 3.4 4.6 5.56 6.84 100-200 1.84 2.32 2.24 2 1.52 200-300 1.36 1.2 0.96 0.72 0.48 300-400 0.96 0.72 0.56 0.4 0.32 400-500 0.64 0.4 0.24 0.32 0.08 500-600 0.4 0.32 0.24 0.08 0.16 600-700 0.4 0.16 0.16 0.08 0.08 700-800 0.32 0.16 0.16 0.08 0 800-900 0.16 0.16 0.08 0.16 0 900-1000 0.24 0.08 0 0.08 0.08
Table 4.24 describes the change in Pk-Pk voltage for each 100 K ohm resistance band. It
is clear from the data obtained that PZT is temperature sensitive for particular frequency
and resistance range. For example at room temperature the Pk-Pk voltage was 1.4 V at 50
Hz and 1-100 K ohm resistance range. For the same resistance range (1-100K ohm) at
1600C and 50 Hz, the vale noted is 1.88 V. For the same resistance range and at 300 Hz
114
the value changes from 5.72V (at 200C) to 6.84V (at 1600C). The change in voltage for
each resistance band at different frequencies has been shown in Figure. 4.25.
0
1
2
3
4
5
6
7
8
1 2 3 4 5 6 7 8 9 10
Resistance band
Pk-P
k Vo
ltage
(V)
50Hz100Hz150Hz200Hz300
Figure 4.25 Change in Pk-Pk voltage for each 100kΩ band at 1600C
Figures 4.26 to 4.30 show the difference for Pk-Pk voltage between two referenced
temperatures. It is clear from these curves that output voltage at 1600C is always less as
compared to room temperature values. With lesser value of resistance, the output voltage
is high enough and then continuously it is in decreasing order. The gap between two
curves is minute which describe that temperature chance doesn’t effect too much for
ordinary conventional equipments. However this change is highly effective for sensitive
equipments in which these smart materials being used. Therefore care must be taken for
selecting the range of considered variables for the reliability of equipments.
115
0
2
4
6
8
10
12
0 200 400 600 800 1000 1200Resistance in K ohms
Pk-P
k Vo
ltage
in V
olts
At 160CAt 20C
Figure 4.26 Effect of temperature on Pk-Pk Voltage at frequency 50 Hz against change in Resistance
0
2
4
6
8
10
12
0 200 400 600 800 1000 1200Resistance in K ohms
Pk-P
k Vo
ltage
in V
olts
At 160CAt 20C
Figure 4.27 Effect of temperature on Pk-Pk Voltage at frequency 100 Hz against change in Resistance.
116
0
2
4
6
8
10
12
0 500 1000 1500Resistance in K ohms
Pk-P
k Vo
ltage
in V
olts
At 160 CAt 20 C
Figure 4.28 Effect of temperature on Pk-Pk Voltage at frequency 150 Hz against change in Resistance.
0
2
4
6
8
10
12
0 200 400 600 800 1000 1200Resistance in K ohms
Pk-P
k Vo
ltage
in V
olts
At 160CAt 20C
Figure 4.29 Effect of temperature on Pk-Pk Voltage at frequency 200 Hz against change in Resistance.
117
0
2
4
6
8
10
12
0 200 400 600 800 1000 1200Resistance in K ohms
Pk-P
k vo
ltage
in V
olts
At 160 HzAt 20C
Figure 4.30 Effect of temperature on Pk-Pk Voltage at frequency 300 Hz against change in Resistance.
118
4.6.5 Development of a Model
The conversion from mechanical force to electrical signals and from electrical signals to
mechanical excitation can easily be transferred by using piezoelectric materials. The
magnitude of transferring the output is a critical parameter in function output of piezo
devices. Various typical models have been developed and optimized by various
researchers. Butterworth-Van Dyke circuit based on IEEE standard on piezoelectricity
and Manson’s electrical network circuit are two of them [89]. These models have their on
limitations and operating ranges. Sherrit et al [90] proposed another model having the
comparison of previously existed models in thickness mode. There was a very little work
on the effect of frequency and magnitude of input voltage and this area was explored by
Georgiou et al [91] by considering the experimental and theoretical assessments on PZT.
The proposed model addressed the other parameters to demonstrate the effect of
resistance, frequency and temperature on the functional performance in the form of Pk-Pk
voltage. In contrast to the Georgiou model, the existing findings demonstrate the effect of
resistances on the output voltage at various resistance bands from 1kΩ to 1000kΩ
resistance bands.
By considering the data obtained in phase-3 of the experimentation, an exponential model
has been developed which indicates the effect of frequency and resistance band on peak-
peak voltage change (∆V) at two different temperatures.
Data tabulated in Table. 4.21 and 4.24 has been used to draw the exponential curves
between resistance band number and difference in peak-peak voltage at 200C and at
1600C for five selected frequencies. These exponential curves at temperature values have
been shown in Figures 4.31-4.35. Pk-Pk value showed a decreasing exponent trend with
119
the increase in resistance band number. By considering the coefficients A and B,
exponents are drawn against Frequency f in Hz. The coefficients A and B against these
frequencies at 200C and showing an increasing trend indicated in Figure 4.36 and Figure
4.37. Similarly the trend for the exponent at 1600C has been shown in Figures 4.38-4.42.
Their coefficients A and B have been drawn against frequency and shown in Figures 4.43
& 4.44.
An exponential model developed indicating the effect of resistance band number (N) on
peak-peak voltage at 200C and 1600C is as under,
V∆ = BNAe−
Where feA 0035.018.2= and feB 003.023.0= (At 200C)
feA 003.074.2= and feB 003.027.0= (At 1600C)
∆V = is the difference in Pk-Pk voltage at particular resistance band.
N = Resistance band number.
At Room Temperature (200C)
∆V = 2.3378e-0.2501N
R2 = 0.9696
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
1 2 3 4 5 6 7 8 9 10
Resistance Band Number,N
Peak
-Pea
k Vo
ltage
(∆V)
Expon. (50Hz)
Figure. 4.31 Difference in Pk-Pk value against Resistance band number at 50Hz
120
∆V = 3.3779e-0.3352N
R2 = 0.9687
0
0.5
1
1.5
2
2.5
3
1 2 3 4 5 6 7 8 9 10
Resistance Band Number,N
Peak
-Pea
k Vo
ltage
(∆
V)
Expon. (100Hz)
Figure. 4.32 Difference in Pk-Pk value against Resistance band number at 100Hz
∆ V = 4.1737e-0.4122N
R2 = 0.9478
0
0.5
1
1.5
2
2.5
3
3.5
4
1 2 3 4 5 6 7 8 9 10
Resistance Band Number,N
Peak
-Pea
k Vo
ltage
(∆
V)
Expon. (150Hz)
Figure. 4.33 Difference in Pk-Pk value against Resistance band number at 150Hz
121
∆ V = 4.4656e-0.4604N
R2 = 0.9441
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
1 2 3 4 5 6 7 8 9 10
Resistance Band Number,N
Peak
-Pea
k Vo
ltage
(∆
V)
Expon. (200Hz)
Figure. 4.34 Difference in Pk-Pk value against Resistance band number at 200Hz
∆V = 6.2123e-0.6048N
R2 = 0.9506
0
1
2
3
4
5
6
7
1 2 3 4 5 6 7 8 9 10
Resistance Band Number,N
Peak
-Pea
k Vo
ltage
(∆V)
Expon. (300Hz)
Figure. 4.35 Difference in Pk-Pk value against Resistance band number at 300Hz
122
A = 2.1827e0.0036f
R2 = 0.9409
01234567
0 100 200 300 400Frequency, f (Hz)
Coe
ffic
ient
A
Expon. (A)
Figure. 4.36 Exponential coefficient, A against Frequency in Hz at 200C
B = 0.2296e0.0034f
R2 = 0.9613
00.10.20.30.40.50.60.7
0 100 200 300 400
Frequency, f (Hz)
Coe
ffic
ient
B
Expon. (B)
Figure 4.37 Exponential coefficient, B against Frequency in Hz at 200C
123
At 1600C
∆V = 2.7586e-0.2785N
R2 = 0.9459
0
0.5
1
1.5
2
2.5
0 2 4 6 8 10 12
Resistance Band Number,N
Peak
-Pea
k Vo
ltage
(∆
V)
Expon. (50Hz)
Figure. 4.38 Difference in Pk-Pk value against Resistance band number at 50Hz
∆V = 4.164e-0.4077N
R2 = 0.9604
0
0.5
1
1.5
2
2.5
3
3.5
4
0 2 4 6 8 10 12
Resistance Band Number,N
Peak
-Pea
k Vo
ltage
(∆
V) Expon. (100Hz)
Figure. 4.39 Difference in Pk-Pk value against Resistance band number at 100Hz
124
∆V = 5.1224e-0.4966N
R2 = 0.9232
0
0.5
1
1.5
22.5
3
3.5
4
4.5
5
0 2 4 6 8 10 12
Resistance Band Number,N
Peak
-Pea
k Vo
ltage
(∆
V)
Expon. (150 Hz)
Figure. 4.40 Difference in Pk-Pk value against Resistance band number at 150Hz
∆V = 3.4694e-0.4427N
R2 = 0.7944
0
1
2
3
4
5
6
0 2 4 6 8 10 12
Resistance Band Number,N
Peak
-Pea
k Vo
ltage
(∆
V)
Expon. (200Hz)
Figure. 4.41 Difference in Pk-Pk value against Resistance band number at 200Hz
∆V = 6.6136e-0.7014N
R2 = 0.8639
0
1
2
3
4
5
6
7
8
0 2 4 6 8 10 12
Resistance Band Number
Peak
-Pea
k Vo
ltage
(∆
V)
Expon. (300Hz)
Figure.4.42 Difference in Pk-Pk value against Resistance band number at 300Hz
125
A = 2.7351e0.0027f
R2 = 0.5975
01234567
0 100 200 300 400
Frequency, f (Hz)
Coe
ffic
ient
A
Expon. (A)
Figure-4.43 Exponential coefficient, A against Frequency in Hz at 1600C
B = 0.2659e0.0032f
R2 = 0.8603
0
0.2
0.4
0.6
0.8
0 100 200 300 400
Frequency, f (Hz)
Coe
ffic
ient
B
Expon. (B)
Figure-4.44 Exponential coefficient, B against Frequency in Hz at 1600C
The results presented in above stated figures 4.36, 4.37 and 4.43, 4.44 clearly indicate the
same behavior in exponential form but the sensitivity for both case is prominent. This
sensitivity is very much dependent on resistance change as compared to frequency and
temperature change. Model has been validated with repeatability and it can be modified
by changing the magnitudes of existing values for wide range of applications.
126
4.7 Discussions
The objective of the present work was to explore the unattended characteristics of
thin lead zirconate titanate piezoelectric ceramics disc during thermal cycling/shocking.
Thermal cycling at different water conditions in various environments has been carried
out. Where as the thermal shocking has been done in de-ionized water. Qualitative
extensive data has been obtained by tedious and lengthy experiments by using the reliable
instrumentations. The aim was to analyze the change in critical properties of above stated
material on its functioning and output performance. Three types of experimentation, each
having its own importance in exploring the properties of PZT material have been
conducted. Frequency of maximum impedance and frequency of minimum impedance of
piezoelectric ceramics material is an important measuring criterion for calculating the
other piezoelectric parameters, like coupling factors, and mechanical quality factor Q.
Significant findings are presented in the subsequent sections.
4.7.1. Effect of Water on PZT Disc
There are many engineering applications where mechanical vibrations convert to
electrical signals. Piezoelectric crystals generate ultrasonic waves in solids and detect
these mechanical waves. The piezoelectric crystals excited by an ac source generate
ultrasonic waves at certain frequencies and converted to electrical signals and can be
displaced on oscilloscope.
A lead zirconate titanate (PZT) ceramics disc was used to investigate the performance
characteristics when exposed to three different solutions; ordinary water, de-ionized
water and a solution of NaCl. The PZT was subjected to thermal cycles in the solutions at
127
800C and changes in the peak to peak voltages were observed.. The change in voltage
may affect the actuating and sensing capability of the instrument in which they are used.
The present work consist a qualitative data to design the smart structures used under such
applications. By considering the above discussion, it is concluded that PZT thin disc is
sensitive in performance characteristics in various solutions at different frequencies. The
changes in potential across the PZT ceramic can be attributed to the out put functional
performance of the ceramic in different water conditions.
4.7.2. Thermal Cycling/Shocking of Thin PZT Disc [From 1000C (Thermal
chamber) to 200C (In de-ionized water)]
Thermal shocking is one of the major causes of degradation of piezoelectric materials. A
thin lead zirconate titanate disc has been analyzed during thermal shocking from 1000C to
200C in de-ionized water. Dielectric constant and coupling factor has been measured by
using the capacitance and frequency of maximum and minimum impedance values
obtained by precise instrumentations. Resonance and anti resonance frequencies are the
measure of electromechanical coupling factor. The coupling between the electrical
excitation and mechanical vibrations determine its piezoelectric effect. Mechanical
vibrations appears like a series LCR circuit to the ac source. This LCR circuit has
minimum impedance at certain frequency and is called resonance frequency. This LCR
circuit has another frequency on the other end which is at maximum impedance and is
called anti-resonance frequency. An extensive study and analysis have been taken in
thermal shocking of PZT disc. The behavior of change in capacitance value is frequency
dependent. The measurement taken at 1 KHz shows no remarkable change in its
128
capacitance value, where as the values obtained at frequency of maximum and at
frequency of minimum impedance showing a remarkable change in its capacitance,
impedance and dielectric values. The capacitance value decreasing continuously by
thermal shocking at fm and a reverse effect is at fn. Dielectric constant at fm decreases by
increasing number of shocks and is an expected normal behavior. Thermal shocking
changes dipole length and causes re-orientations of these dipoles which attributes to the
changes in capacitance and dielectric constant of the material. Effective and transverse
coupling factors are continuously increasing. The difference in frequency of maximum
and minimum impedance is widening throughout which resulted in an increases of
coupling factor. This increase in coupling factor is thought to be due to lesser shocking
temperature difference. Further experimentation is recommended with high temperature
difference in thermal shocking. The properties of the materials degrade with the change
in environment. Earlier studies described that piezo material are temperature and
frequency sensitive. The critical temperature where these piezo properties should change
is the curie temperature, but it is observed in present work that thermal shocking is a
severe cause of the degradation of these properties even well below the curie temperature.
The description of dielectric constant is very difficult in thermal cycling problems
because the orientations of molecular size dipoles changes frequently in such shocking
conditions. Theory becomes more difficult because of electrostatic interaction between
dipoles. However, the measurement of fm and fn is one of the reliable methods to
determine the capacitance value at particular frequency. The relative difference in the
frequencies of maximum and minimum impedance depends on both the material coupling
factor and resonator geometry.
129
Effective ionic size and the forces in ceramics crystals are temperature dependent and
may change a particular temperature to a new structure. The small ionic movement is
capable of change in properties of the piezocrystals. Change in dimension occurs due to
thermal cycling/ shocking and resulted in change in ionic size orientation of dipoles.
Piezoelectric undergoes a spontaneous displacement of ions below the curie temperature
due to thermal cycling and elongate the basic structure. The polarization direction may
alter the properties of the piezoelectric ceramics. The development of the parameter
dipole moment involves long range interaction energy lower by re-arrangement of these
ions. When the temperature difference increase the ions become shifted, which change its
polarization. This change in polarization further causes of degradation in capacitance and
dielectric properties of the material.
Increase in dielectric constant at 1 KHz is very less as compared to the decrease in its
value at frequency of maximum impedance. The increasing value of transverse and
longitudinal coupling factor is a an interesting finding and it is observed that the thermal
shocking in de ionized water increase the capability of converting electrical energy to
mechanical energy and vise versa. This effect may useful in designing of oscillators and
sensors.
130
4.7.3 Thermal Cycling/Shocking of Thin PZT Disc from 1000C&1500C (Thermal
chamber) to 200C (In de-ionized water)
This part of the work was done to analyze the sensitivity of thin PZT in thermal
shocking at two different temperatures. The tests conducted at 200C and 1600C and a
comparative analysis have been conducted to investigate the effect of temperature on
piezoelectric properties. Values for dielectric constant, coupling factor and modulus of
impedance are greatly affecting with the number of cycle as well as by changing the
shocking conditions.
The change in fm and fn causes the change of mechanical quality factor. This response of
the material can be utilized in designing of oscillators. It is observed that the difference in
these two stated frequencies (fm & fn) is small as compared to their impedance peaks
during thermal shocking. The results suggest that the PZT ceramic suffers a noticeable
change in polarization when exposed to repeated heating and quenching cycles well
below the curie temperature (350oC) for the PZT ceramic. It is thought that significant
depolarization of the PZT ceramic occurs due to the disorientation of the ferroelectric
domains and this re-orientation is affecting the critical piezoelectric properties by thermal
shocking and quenching. The behavior is normal but the number of peaks has been
increased due to expected change in length and the re-orientation of the dipoles. The
development of the dipole moments by thermal shocking is due to the interaction
between the ions in the unit cells of the crystal geometry. When these ions displaced, the
energy of the crystals decreases. This decrease in energy and ionic movement displace
the dipole moment and may result in the form of piezoelectric crystals degradation in its
properties. At fm, the PZT crystals can be used as filters with high mechanical quality
131
factor. Between fm and fn the response controlled by the mass of the crystal. This property
can be utilized in the designing of oscillators. Higher is the difference between these two
frequencies, higher is the coupling factor. This increase in coupling factor is a measure of
the efficiency of converting mechanical energy to electrical energy and and electrical
energy to mechanical energy.
4.7.4. Effect of Frequency and Resistance on peak-peak voltage in Thermal
Conditions
A long series of experimentations have been performed in this phase. The effect
of frequency and resistance has been observed for the output voltage across the thin PZT
disc. By observing the results, it can be stated that thin PZT disc is relatively less
sensitive in its output performance at two different temperature conditions (i.e..1600C
&200C). For both conditions, the peak-peak voltage value was higher at lower
frequencies but interestingly, the difference in peak-peak voltage for a particular
resistance band behaved differently. At a particular resistance band and frequency for two
temperatures, the change in voltage indicates that temperature also influencing the
performance characteristics of thin disc. At higher frequencies, the maximum drop in
voltage was observed at low resistance as compared to at low frequency drop. Another
interesting behavior observed that after 400 KΩ resistances the peak-peak voltage
observed is approximately constant even at higher frequencies. The model developed in
section 4.5.5 indicates very useful results those can be utilized for the modeling of smart
piezoelectric devices working in these particular ranges. Model shows that PZT disc is
relatively temperature sensitive and the coefficient values are frequency dependent.
132
CHAPTER #5
CONCLUSIONS AND FUTURE RECOMMENDATIONS
5.1 Conclusions
Fatigue behavior of piezoelectric materials either by electrical, mechanical,
electromechanical or thermal cycling /shocking is still a field of recent research. Analysis
of these smart materials has a great scope for further research in many directions. The
current research work is a unique finding and effort in the field of piezoelectric materials
under thermal cycling condition. In literature review section importance and need of
work has been elaborated
The study shows that the performance characteristics are sensitive to the type of solution
in which the PZT was immersed. The drop in potential in heating cycle is greatest in
NaCl solution followed by ordinary tap water and least in de-ionized water. The time in
regaining the peak to peak voltage was longer by the NaCl solution followed by de-
ionized water and then the least time was observed in ordinary tap water. These changes
are thought to be attributed to the presence of ions and solid residue which adheres to the
surface of the PZT ceramic and evaporate during the drying stage after a specific time
depending on frequency of excitation.
The work indicates the effect of thermal shock and quenching in de-ionized water and the
degradation in piezoelectric thin PZT disc. Thermal shocking is one of the severe causes
for the change in dipole lengths and directions which changes its capacitance and
dielectric constant values. All measured values can be used to calculate the other
piezoelectric parameters and Mechanical Q factor for the piezo specimens.
133
During thermal shocking, the decrease in energy and ionic movement displace the dipole
moment and may result in the form of piezoelectric crystals degradation in its properties.
At fm, the PZT crystals can be used as filters with high mechanical quality factor.
Between fm and fn the response controlled by the mass of the crystal. This property can be
utilized in the designing of oscillators.
The model developed in section 4.5.5 indicates very useful results those can be utilized
for the modeling of smart piezoelectric devices working in these particular ranges. In this
model it is concluded that thin PZT disc is relatively more sensitive in resistance change
as compared to temperature and frequency change.
134
5.2 Future Recommendations
1. Thermal cycling of piezoelectric specimens has been determined in various water
condition and their affects on performance characteristics are noticeable in
previous findings. On the basis of these findings, following future
recommendations are noted as:
• To check the performance characteristic on other grades and sizes of the
piezoelectric materials.
• To investigate the behavior at higher temperature rather than the lower as
considered in present work.
• To determine the behavior in other designed circuits at higher frequencies.
• To investigate the sensitivity analysis and optimization by using the
standard techniques.
• To perform the experimentation by considering the other environments
and solutions.
2. There are many engineering applications where mechanical vibration converts to
electrical signals. Thermal shocking in de ionized water shows very informative
and important results and there is a great scope of work in this area as under.
• To investigate the various piezoelectric parameters at higher thermal
shocking temperature.
• To investigate the stress corrosion cracking of piezoelectric ceramics in
water.
• Interaction and reliability of electromechanical coupling in water and air.
135
• Investigations are recommended at above or near to curie temperature.
• Affect of impedance, dielectric loss, and other compliances are required to
investigate for further measurements and characteristics of these materials.
• Determination of stress intensity factor by using fracture mechanics
techniques.
• Modeling and designing of equipments is recommended to investigate the
performance characteristics and sensitivity by using available commercial
software’s for reliability and validation of electromechanical systems.
• Affect of properties on PZT by variation of temperature from very low to
high is another area, which is under investigation and may be useful for
numerous sophisticated applications.
• Material characteristics are key factor in material selection of electronic
equipments. Most components are required with their high dielectric
constant. Before selection of particular grade and size of piezoelectric
material, it is recommended to select the optimized frequency and
temperature for maximum performance output.
3. To develop a center of study for the analysis of electronics and smart materials
used in micro electro-mechanical systems in Mechanical Engineering Department
University of Engineering and Technology Taxila.
136
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APPENDIX-A
THERMAL CYCLING/SHOCKING RESULTS IMAGES OF THIN PZT DISC
Testing/Measurements Following testing were measured in thermal shocking test
1. Thermal shocking from 1000C from thermal chamber to de-ionized water at 200C. 2. Thermal cycling test between 1000C and 900C for 60 cycles in step of 10 cycles.
3 Shocked once for 60Cycles between 1000C and 900C 4. Thermal shocking from 1500C from thermal chamber to de-ionized water at 200C.
All of the above enlisted tests were performed and tested specimens were analyzed by using impedance analyzer along with test fixture. The figures below shows behavior of thin PZT disc during above stated testing in the form of capacitance, Impedance, Dissipation factor and Phase angle in different conditions.
1. Thermal shocking from 1000C from thermal chamber to de-ionized water at 200C.
A-1 Original value of Capacitance (Cp) of thin disc at 1 KHz
A-2 Original value of Impedance (Z) at 1 K Hz
A-3 Original value Cp atFrequency of Maximum Impedance (fm)
A-4 Original value of Cp at Frequency of Minimum Impedance (fn)
A-5 Original value of Impedance (Z) at Frequency of maximum
impedance
A-6 Original value of Z at Frequency of Minimum Impedance
TEST-1 After Five Shocks A-7 Cp at Frequency of Maximum Impedance
A-8 Cp at Frequency of Minimum Impedance
A-9 Impedance at fm
A-10 Impedance at fn
TEST-4 After Twenty Shocks A-11 Cp at 1 KHZ
A-12 Z at 1 KHz
A-13 Cp at fm
A-14 Cp at fn
A-15 Z at fm
A-16 Z at fn
TEST-5 After Twenty Five Shocks A-17 Cp at 1 KHz
A-18 Z at 1 KHz
A-19 Cp at fm
A-20 Cp at fn
A-21 Z at fm
A-22 Z at fn
TEST-6 After Thirty Shocks A-23 Cp at 1 KHz
A-24 Z at 1 KHz
A-25 Cp at fm
A-26 Cp at fn
A-27 Z at fm
A-28 Z at fn
TEST-7 After Thirty Five Shocks A-29 Cp at 1 KHz
A-30 Z at 1 KHz
A-31 Cp at fm
A-32 Cp at fn
A-33 Z at fm
A-34 Z at fn
2. Thermal cycling test between 1000C and 900C for 60 cycles in step of 10 cycles.
In this series of experimentations, the PZT discs were observed for their sensitivity analysis during thermal cycling to observe their stepped thermal cycling and continuous thermal cycling between very narrow ranges of thermal change. The specimens were heated to 1000C and then cycled between 1000C and 900C for ten cycles. The discs were then taken to measure their capacitance and impedance values as described in their relative figures. Values measured after every ten such cycles and total 60 cycles were analyzed in a step of ten cycles.
A-35 Original values of Cp at 1 KHz
A-36 Original value of Z at 1 KHz
Test-1 From 1-10 cycles between 1000C and 900C. A-37 Cp at 1 KHz (1-10 continuous cycles)
A-38 Z at 1 KHz (1-10 continuous cycles)
A-39 Cp at fm (1-10 continuous cycles)
A-40 Cp at fn (1-10 continuous cycles)
A-41 Z at fm
A-42 Z at fn
Test-2 From 10-20 cycles between 1000C and 900C. A-43 Cp at 1 KHz (10-20 continuous cycles)
A-44 Z at 1 KHz (10-20 continuous cycles)
A-45 Cp at fm
A-46 Cp at fn
A-47 Z at fm
A-48 Z at fn
Test-3 (21-30 cycles between 1000C and 900C)
A-49 Cp 1 KHz
A-50 Z at 1 KHz
A-51 Cp at fm
A-52 Cp at fn
A-53 Z at fm
A-54 Z at fn
Test-4 (31-40 cycles) A-55 Cp at 1 KHz
A-56 Z at 1 KHz
A-57 Cp at fm
A-58 Cp at fn
A-59 Z at fm
A-60 Z at fn
Test-5 (41-50 cycles) A-61 Cp at 1 KHz
A-62 Z at 1 KHz
A-63 Cp at fm
A-64 Cp at fn
A-65 Z at fm
A-66 Z at fn
Test-6 (51-60 cycles) A-67 Cp at 1 KHz
A-68 Z at 1 KHz
A-69 Cp at fm
A-70 Cp at fn
A-71 Z at fm
A-72 Z at fn
3. Shocked once 0Cycle-60Cycles A-73 Cp at 1 KHz
A-74 Z at 1 KHz
A-75 Cp at fm
A-76 Cp at fn
A-77 Z at fm
A-78 Z at fn
4. Thermal shocking from 1500C from thermal chamber to de-ionized water at 200C.
After Five Shocks
A-79 Cp at 1 KHz
A-80 Z at 1 K Hz
A-81 Cp at fm
A-82 Z at fm
A-83 Z at fn
After Fifteen Shocks A-84 Cp at 1 KHz
A-85 Z at 1 KHz
A-86 Cp at fm
A-87 Cp at fn
A-88 Z at fm
A-89 Z at fn
After Twenty Five Shocks A-90 Cp at 1 KHz
A-91 Z at 1 KHz
A-92 Cp at fm
A-93 Cp at fn
A-94 Z at fm
A-95 Z at fn
After Thirty Five Shocks A-96 Cp at 1 KHz
A-97 Z at 1 KHz
A-98 Cp at fm
A-99 Cp at fn
A-100 Z at fm
A-101 Z at fn
Appendix-B
List of Pertinent PhD Publications
1. Riffat Asim Pasha, M.Z.Khan, “Recent Developments in Piezoelectric Ceramics Materials and Deteriorations of their Properties” Proceedings of 2nd International Conference on Frontiers of Advanced Engineering Materials (FAEM-2006) pp. 13-19.
2. Riffat Asim Pasha, M.Z.Khan, A.M.Hashmi, “Experimental Procedure of
Frequency Determination in Piezoelectric Ceramics Materials, Al-Azhar University Engineering Journal, Vol.2, No. 4. pp. 380-388 (AEIC- 2007) Cairo, Egypt.
3. Riffat Asim Pasha Zahid Suleman and M. Z. Khan, “Analysis of Thickness Effect
on Piezoelectric Beam” Proceedings of Failure of Engineering Materials and Structures, pp. 59-63 (FEMS-2007)
4. Riffat Asim Pasha, M.Z.Khan, “Thermal Shocking of a Thin Lead Zirconate
Titanate Piezoelectric Ceramics disc, Proceedings Pakistan Academy of Science, 46(1): pp. 47-52 2009 (HEC Recognized).
5. Riffat Asim Pasha, M.Z.Khan, “Performance Characteristics of a Lead Zirconate
Titanate Piezoelectric Ceramic Disc in Water, Accepted for publication in M.U Research Journal of Engineering and Technology, 2009 (HEC Recognized).
6. Riffat Asim Pasha, Muhammad Zubair Khan, “Effect of Thermal Shocking and
Quenching on the Degradation Behaviour of a Thin PZT Disc, Pakistan Journal of Scientific and Industrial Research,2010 53(1) p. 1-5 (HEC Recognized)