Post on 01-Mar-2018
90
CHAPTER 4
GROWTH AND CHARACTERIZATION OF DYES AND
AMINO ACID DOPED GLYCINE PHOSPHITE SINGLE
CRYSTALS
4.1 INTRODUCTION
Different combination of amino acids and inorganic acids lead to
invention of new crystal family with excellent ferroelectric properties.
Examples of such combinations are triglycine sulphate, triglycine selenate,
triglycine fluoberyllate, betaine phosphite and Glycine Phosphite (Alemany
et al 1973, Song et al 2000, Lines and Glass 1977, Albers et al 1988). Growth
and characterization of pure and thiourea doped GPI crystals were
investigated by several researchers (Deepthy and Bhat 2001, Kalainathan et al
2005, 2006). Doping of dyes in organic crystals such as KDP, KAP, bis
glycine cadmium chloride and L-arginine phosphate were reported to
understand the optical, thermal, NLO, laser applications and mechanical
properties of the materials (Monica Enculescu 2009, Pritula et al 2009,
Velikhov et al 2007, Kumaresan et al 2008, Raju et al 2011, Shivani Singh
and Bansi Lal 2008). Numerous efforts were made on the growth,
pyroelectric and ferroelectric properties of amino acid doped TGS crystals
(Lock 1971, Bye et al 1973, Alexandru et al 2004, Raghavan et al 2008,
Nakatani et al 2008, Meera et al 2000, 2001, 2004). Efforts were also made on
combinations of doping such as urea, yttrium sulfate, L-serine + cobalt
sulfate, and L-alanine + urea with TGS crystals. These combinations
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effectively increase dielectric, pyroelectric, ferroelectric and mechanical
properties of the material (Jiann-Min Chang et al 2002, Jan Novotny et al
2003). Influence of L-Alanine and D-Alanine dopants on TGS improves the
ferroelectric and pyroelectric stabilities (Berbecaru et al 2005). Hence dyes
doped KDP and amino acid doped TGS crystals play a major role in
improving physical properties of the materials. Since GPI is the hydrogen
bonded ferroelectric material like TGS and soft ferroelectric material as that
of KDP crystals, in the present investigation, organic dyes such as rhodamine-
B, malachite green and fluroscein and amino acid (L-Proline) were doped
with pure GPI crystals to analyze the growth and physical properties of the
materials.
4.2 BULK CRYSTAL GROWTH
The impurity content of synthesized GPI was minimized by
purifying the solution by repeated recrystallization. In this study, 0.5 mol %
of organic dyes such as rhodamine-B, malachite green and fluroscein and 3
mol % amino acid (L-Proline) were doped with pure GPI crystals. Growth
runs were carried out from solution saturated at 45o C according to the
nucleation kinetic data, it is feasible to grow bulk crystals in 45o C to 40o C
range. The saturated solution was further purified by Wattman filter paper (42
grades). Before starting the growth, to ensure the homogenization of the
solution, it was heated to a few degrees above the saturation temperature. The
temperature was reduced at the rate of 0.2o C / day as the growth progressed.
The seeds obtained from slow evaporation were employed for the growth. The
test seed was used and seasoned at the growth temperature before initiating
the growth. Once the growth was initiated, the good quality (100) oriented
seeds were used for the growth. The period of growth ranges from 30 to 35
days. After the completion of growth, crystals were harvested. The grown
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crystals were found to be non-hygroscopic. The crystal dimensions of RB-
GPI, M.grn-GPI, Flrn-GPI and L.Prol-GPI are 18 mm × 16 mm × 10 mm, 13
mm × 10 mm × 8 mm, 20 mm × 12 mm × 10 mm and 30 mm × 24 mm × 14
mm respectively and are shown in Figure 4.1.
(a) (b)
(c) (d)
Figure 4.1 As grown crystals of (a) Rhodamine-B and (b) Malachite
green doped GPI by solvent evaporation method and
(c) Fluorescein and (d) L-Proline doped GPI grown by slow
cooling method
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4.3 RESULTS AND DISCUSSION
4.3.1 Single Crystal X-Ray Diffraction Analysis
Unit cell parmeters of dyes and amino acid doped GPI crystals were
determined by single crystal X-ray diffraction studies using ENRAF NONIUS
CAD 4 single crystal X-ray diffractometer with MoK ( =0.717 ) radiation
at room temperature. The crystal specimens of dimension 4×3×3 mm3 were
used for the analysis. Least-square refinement of 135, 163, 225 and 130
reflections were made for rhodamine-B, malachite green, fluorescein and L-
Proline doped GPI crystals respectively and the structure was solved by direct
method and refined by the full matrix least-square technique using the
SHELXL program. Dyes and amino acid doped GPI belong to monoclinic
structure with the space group P21/a at room temperature i.e in paraelectric
phase. The lattice parameters of pure and rare earth metals doped GPI crystals
were presented in Table 4.1. It was observed that volume of the doped
crystals decreased which attributes to the lattice strain by means of dyes and
amino acid as dopants.
Table 4.1 Lattice parameters of pure, dyes and amino acid doped GPI
crystals
CellParameters /
CrystalName
a (Å) b (Å) c (Å) V (Å3)
Pure GPI 7.391(2) 8.477(3) 9.774(4) 90o 100.48 o 90o 616
R.B-GPI 7.381(7) 8.441(8) 9.751(9) 90o 100.55 o 90o 597.3
M.grn-GPI 7.395(6) 8.474(7) 9.763(8) 90o 100.45 o 90o 601.7
Flrn-GPI 7.375(8) 8.446(11) 9.743(11) 90o 100.45 o 90o 596.8
L.Prol-GPI 7.378(8) 8.462(9) 9.753(10) 90o 100.35 o 90o 599
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4.3.2 Powder X-Ray Diffraction Analysis
The powder X-ray diffraction pattern for dyes and amino acid
doped GPI crystals was recorded using SEIFERT JSO DEBYE FLEX 2002
diffractometer. The powdered samples of grown crystals were subjected to
intense X-rays of wavelength 1.5405 Å (CuK ) at scan speed of 1o/ min. The
powder diffraction pattern of pure, dyes doped GPI crystals are shown in
Figure 4.2. The changes in the relative intensity and peak position of the
pattern confirm the incorporation of dyes in pure GPI crystal. The intensity of
rhodamine-B doped GPI was predominantly suppressed as shown in Figure
4.2 and most of the planes after 30o were diminished in the case of malachite
green and fluorescein doped GPI samples.
20 30 40 50 600
200
400
600
0
10
20
30
400
200
400
600
8000
100
200
300
400
500
(402
)
(33-3
)
(30
3)
(14
1)
(302)
(320)
(13
2)
(11-4
)
(023)
(103
)
(013
)
(21
-1)
(11
2)
(20-1
)(1
20)
(11
-2)
(10
-2)
Degree (2 )
GPI
(12
-1)
(143)
(410
)
(32
1)
(30
-3)
(13
-2)
(211
)(2
01)
(21
-1)
(112)
(120
)
(11-2
)(0
20)In
ten
sit
y (
arb
.un
its
)
R.B-GPI
(112
)
(21
1)
(12
0)(1
1-2
)
M.grn-GPI
(13
3)
(21
1)
(112)
(120
)(1
1-2
)
Flrn-GPI
Figure 4.2 Powder XRD pattern of Pure, Rhodamine-B, Malachite
green, and Fluorescein doped GPI crystals
95
4.3.3 Crystalline Perfection Analysis
Crystalline Perfection of dyes and amino acid doped GPI crystals
were carried out by High resolution X-ray diffractometer. Figure 4.3 shows
the HRXRD rocking curves recorded for rhodamine-B and malachite green
doped GPI single crystal specimens.
-200 -100 0 100 2000
600
1200
1800
2400R-B-GPI
(120) Plane
MoK
Diffr
acte
d X
-ra
y in
ten
sity [
c/s
]
Glancing angle [arc sec]
60"
27"56"
(a)
-150 -100 -50 0 50 100 1500
800
1600
2400
Diffr
acte
d X
-ra
y in
ten
sity [
c/s
]
Glancing angle [arc sec]
40"
25"
M.Grn-GPI
(120) Plane
MoK
30"
(b)
Figure 4.3 X-Ray Rocking curve of (a) Rhodamin-B and (b) Malachite
green doped GPI crystals
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The solid line (convoluted curve) was well fitted with the
experimental points represented by the filled circles. On deconvolution of the
diffraction curve, it was clear that the curves contain additional peaks, which
are 60 and 40 arc sec away from the main peak for rhodamine-B and
malachite green doped GPI crystals respectively. These additional peaks
depict an internal structural very low angle boundary. The angular separation
between the two peaks gives the tilt angle ‘ ’ which was 60 and 40 arc sec for
rhodamine-B and malachite green doped GPI crystals respectively for the
specimens depicted in Figure 4.3. The full width at half maximum of the main
peak and the very low angle boundary are respectively 56 and 27 arc sec for
rhodamine-B-GPI and 30 and 25 arc sec for malachite green-GPI crystals.
These low values reveal the fact that both the regions of the crystal are nearly
perfect as one can expect such low values only for crystals with reasonable
quality. Though the specimen contains a very low angle boundary, the
relatively low angular spread of around 200 arc sec of the diffraction curve
and the low FWHM values show that the crystalline perfection is reasonably
good. Thermal fluctuations or mechanical disturbances during the growth
process could be responsible for the observed very low angle boundary.
Figure 4.4 shows the rocking curve recorded for 0.2 mol% of
fluorescein doped single crystal specimen. The RC contains a single sharp
peak and indicates that the specimen is free from structural grain boundaries.
The FWHM of the curve is 20 arc sec which is somewhat more than that
expected from the plane wave theory of dynamical X-ray diffraction
(Batterman and Cole 1964) for an ideally perfect crystal. The broadening of
rocking curve without the presence of any splitting can be attributed to variety
of defects like randomly oriented mosaic blocks, dislocations, Frankel defects,
implantation induced defects (due to simultaneous existence of vacancies as[
97
Figure 4.4 X-Ray Rocking curve of Fluorescein doped GPI crystal
well as interstitial defects) etc. But depending upon the nature of asymmetry,
as investigated in our earlier as well as recent articles, one can expect
predominant occupation of vacancy or interstitial defects (Krishan Lal and
Bhagavannarayana 1989, Bhagavannarayana et al 2005b, 2008, 2010, 2011a,
Kushwaha et al 2010, Bhagavannarayana and Kushwaha 2010) which can be
realized in the following way. For a particular angular deviation ( ) of
glancing angle with respect to the peak position, the scattered intensity is
much more in the negative direction in comparison to that of the positive
direction. This feature clearly indicates that the crystal contains
predominantly vacancy type of defects than that of interstitial defects. This
can be well understood by the fact that due to vacancy defects which may be
due to fast growth (Bhagavannarayana et al 2010), as shown schematically in
the inset, the lattice around these defects undergo tensile stress and the lattice
parameter d (interplanar spacing) increases and leads to give more scattered
(also known as diffuse X-ray scattering) intensity at slightly lower Bragg
angles ( B) as d and sin B are inversely proportional to each other in the
Bragg equation (2d sin B= n ; n and being the order of reflection and
wavelength respectively which are fixed). However, these point defects with
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much lesser density as in the present case hardly give any effect on the
performance of the devices based on such crystals. More details may be
obtained from the study of high-resolution diffuse X-ray scattering
measurements (Bhagavannarayana et al 2005). If the concentration is high,
the FWHM would be much higher and often lead to structural grain
boundaries (Bhagavannarayana et al 2008). Point defects up to some extent
are unavoidable due to thermodynamical considerations and growth
conditions (Bhagavannarayana et al 2010).
Figure 4.5 shows the rocking curve recorded for, 3 mol% of
L-proline doped crystal specimen. The rocking curve was quite sharp without
any satellite peaks which may otherwise be observed either due to internal
structural grain boundaries (Bhagavannarayana et al 2005) or due to epitaxial
layer which may sometimes form in crystals grown from solution
(Bhagavannarayana et al 2006). FWHM of the rocking curve was 7.5 arc sec
for L-proline doped GPI crystal which was very close to that expected from
the plane wave theory of dynamical X-ray diffraction (Batterman and Cole
1964).
-200 -100 0 100 2000
1000
2000
3000 L-Prol-GPI
(120) Plane
MoK
Dif
fracte
d X
-ray i
nte
nsit
y [
c/s
]
Glancing angle [arc sec]
7.5"
Figure 4.5 X-Ray Rocking curve of L-Proline doped GPI crystal
99
4.3.4 Optical Spectral Analysis
The UV–Vis NIR spectrum was recorded using SHIMADZU
UV-Spectrometer 1601 in the range of 200 to 1100 nm. Optically polished
crystal plates of 2 mm thickness were used for the measurement. The
recorded spectra of dyes doped GPI are shown in Figure 4.6. The
transmittance of rhodamine-B and malachite green doped GPI crystals were
reduced to 50 % and 45 % respectively as the dyes have strong absorption in
the visible range. The absorption of 787 and 658 nm in rhodamine-B and
malachite green and doped GPI crystals respectively indicates that the
incorporation of dyes in pure GPI crystals.
Figure 4.6 UV-Visible Spectra of Pure, Rhodamine-B and Malachite
green doped GPI crystals
100
4.3.5 Raman Spectroscopic Analysis
The various functional groups of pure and L-Proline doped GPI
crystals were identified by Raman spectroscopic analysis using standard
Raman spectrometer. Recorded Raman spectrum is shown in Figure 4.7.
291
412
507
558
647
713
871
955
1032
1267
1313
1420
1540 1718
296 412
509
558
647
723
869
955
1031
1267
1314
1417
1542
1616
1655
1718
200 400 600 800 1000 1200 1400 1600 1800
0
200
400
600
800
Wavenumber (cm-1)
Pure GPI
0
200
400
600
800
1000
Ram
an
In
ten
sit
y (
arb
.un
its)
L.Prol-GPI
Figure 4.7 Raman Spectra of Pure and L-Proline doped GPI crystals
The most characteristic stretching mode ( CO) of the C=O bond
appears at 1718 cm 1. The bands in the region between 1150 and 900 cm 1
arise from the stretching vibrations of the PO3 groups and bending (in-plane
and out-of-plane) vibrations of the P–H bond. The deformation modes of the
101
PO3 group of the phosphite ions appear in the region between 600 and
400 cm 1, where the bands of the deformation (wagging and rocking) modes
of the COOH group also appear. The bonds observed at 1655 and 1616 cm-1
corresponds to C=O and NH of L-Proline molecule. This clearly indicates
the incorporation of L-proline in pure GPI crystal. The symmetric stretching
vibration of NH3+ was observed at 1540 cm-1 and 1542 cm-1 for pure and
doped GPI. Scissoring vibrations of CH2 bond was observed at 1420 and
1417 cm 1. The band at 1313 and 1314 cm 1 was assigned to the twisting
mode of CH2 vibration. The symmetric vibration of the PO2 was identified at
955 cm 1 from the spectrum. Bending mode of PH bond was found at
1031 cm 1. The band at 869 cm 1 was assigned as the stretching mode of CC
bond. Deformation vibrations of the COOH group of glycinium was observed
at 647 cm 1.Wagging and rocking vibrations of the same group were observed
at 558 and 509 cm 1. Raman shift at 412 cm 1 was assigned as the
deformation vibrations of phosphite ions and all the peak assignments are
given in Table 4.2.
Table 4.2 Assignments of Raman spectrum
Raman shift (cm-1)Pure GPI L.Prol-GPI
Assignments
1718 1718 C=O---- 1665 C=O---- 1616 NH
1540 1542 sNH3
1420 1417 CH2
1313 1314 CH2
1267 1267 C-OH1032 1031 PH955 955 sPO2
871 869 CC647 647 COOH558 558 COOH507 509 COOH412 412 sPO3
102
4.3.6 Ferroelectric Transition Temperature Analysis
Differential scanning calorimetric measurement was used to
determine the ferroelectric transition temperature of dyes and amino acid
doped GPI crystals using NETZSCH DSC 204 differential scanning
calorimeter with a cooling / heating rate of 10 K/min. DSC spectrum was
recorded in nitrogen atmosphere and is shown in Figure 4.8. An endothermic
peak at 215, 227, 226 and 236 K was observed for rhodamine-B, malachite
green, fluorescein and L-Proline doped GPI crystals respectively, which
corresponds to second-order ferroelectric transition temperature of the
materials. Thus the transition temperature was increased considerably for dyes
and amino acid doped crystals except rhodamine-B doped GPI crystal.
210 215 220 225 230 235 240 2450.35
0.36
0.37
0.36
0.38
0.36
0.37
0.30
0.32
Temperature (K)
R.B-GPI
215 K
227 K
M.green-GPI
226 K
Flrn-GPI
Heat
flo
w (
mW
/mg
)
236 K
L.Prol-GPI
Figure 4.8 DSC curve of dyes and amino acid doped GPI crystals
103
4.3.7 Piezoelectric Charge Co-efficient Measurements
Piezoelectric d33 charge coefficient for dyes and amino acid doped
GPI crystals were carried out using a Precision Piezo Meter System PM 300.
Piezo Meter was calibrated with the dynamic force of 0.25 N and the
frequency of 110 Hz. Force applied and piezoelectric charge was measured
along the (100) plane of the crystal plates. Piezoelectric d33 coefficients were
determined. Effect of poling (an electric field of 10 kV / mm for 10 minutes
duration was given to the samples) of crystals was also carried out.
Piezoelectric charge coefficients of dyes and amino acid doped GPI (unpoled
and poled) crystals were presented in Table 4.3.
Table 4.3 Piezoelectric charge coefficients (d33) of pure, dyes and amino
acid doped GPI crystals
d33 (pC/N)Crystal Before
PolingAfter DC
Poling
Pure GPI 0.87 1.03
Rhodamine B-GPI 0.30 0.56
Malachite green-GPI 0.49 0.53
Fluorescein-GPI 0.57 0.66
L-Proline-GPI 0.27 0.33
4.3.8 Ferroelectric Measurements
Ferroelectricity of the material is ascertained by P – E hysteresis
loop. Hysteresis loop (Figure 4.9) was traced for dyes and amino acid doped
GPI crystals using automatic P – E loop tracer at the temperature of 193 K
and at frequency of 50 Hz. The experiment was performed on ferroelectric
b-axis oriented (100) crystal plates of thickness 3 mm. Observed hysteresis
104
loops in present investigation are in elliptical shape which shows the
ferroelectric nature of the materials. Area of the hysteresis curve increases
along with the remanent polaristaion and coercive force with increase of
applied electric field. The squareness of hysteresis loop was determined. The
squareness parameters for rare earth metals doped crystals were found to be
nearer to 2. The ferroelectric parameters were calculated and presented in
Table 4.4.
Electric Field (kV/cm)
-15 -10 -5 0 5 10 15
Po
lari
zati
on
(µ
C/c
m2)
-8
-6
-4
-2
0
2
4
6
Pure GPI
R-B-GPI
M.grn-GPI
Flrn-GPI
(a)
Electric Field (kV/cm)
-8 -6 -4 -2 0 2 4 6 8
Po
lari
zati
on
(µC
/cm
2)
-10
-8
-6
-4
-2
0
2
4
6
8
10
Pure GPI
L-Prol-GPI
(b)
Figure 4.9 P – E Hysteresis Loop of (a) dyes and (b) amino acid doped
GPI crystals
105
Table 4.4 Ferroelectric parameters of pure, dyes and amino acid doped
GPI crystals
CrystalCoercive
Field‘Ec’ (kV/cm)
RemanentPolarization‘Pr’ µC/cm2)
SaturationPolarization‘Ps’ (µC/cm2)
Squareness ofPolarization
‘Rsq’
Pure GPI 4.73 0.82 1.02 1.90
R.B-GPI 8.71 3.03 3.9 1.88
M.green-GPI 5.91 4.14 5.07 1.92
Fluorescein -GPI
3.61 0.29 0.61 1.58
L.Prol-GPI 4.4 7.12 7.82 2.01
4.3.9 Mechanical Stability Analysis
Crystal hardness is one of the important mechanical properties of
the materials. It can be used as a suitable measure of the plastic properties and
strength of a material. Stillwell (1938) defined hardness as resistance against
lattice destruction whereas Ashby defined it as an ability of a crystal to resist
a structural breakdown under an applied stress (Karan et al 2003). This
resistance is an intrinsic property of the crystal. There are three general types
of hardness measurements depending on the manner in which the test is
conducted. These are scratch hardness, indentation hardness and rebound, or
dynamic hardness. Among these hardness measurement techniques,
indentation hardness testing is frequently used to assess the crystal hardness.
Indentation was made on dyes and amino acid doped GPI crystals
using microhardness tester MVH-1 (METATECH). The applied load was
varied from 5 g to 50 g. The indentation were approximately square in shape.
The shape of the impression is structure, face and also material dependent.
The length of the two diagonals of the indentations were measured by a
calibrated micrometer attached to the eye piece of the microscope after
unloading and the average (d) is found out. The Vickers hardness number is
106
computed using the formula Hv = 1.8544 P/d2 kg/mm2, where P is the applied
load in kilograms, d is the diagonal length of the indentation impression in
micrometers.
The mirohardness plot of dyes and amino acid doped GPI crystals
are shown in Figure 4.10. It was observed from the plot that the hardness
number increases with the load up to 20 g, which shows the work hardening
of the material. After 20 g of load micro cracks were initiated and propagated
with increase of load till 50 g load beyond which crystal gets damaged and the
measurement could not be continued. In comparison with pure GPI hardness
number improved on doping since the absorbance of dyes and amino acid into
the pure GPI lattice hampers the formation of dislocation.
Using the maximum value of hardness number ‘Hv’, the mechanical
parameter such as elastic stiffness constant ‘C11’, meyer’s index ‘n’ and yield
strength ‘ y’ were calculated and presented in Table 4.5.
0 10 20 30 40 50
30
40
50
60
70
80
90
100
110
120
130
140
Ha
rdn
ess
(H
v)
Load (g)
Pure GPI
R.B-GPI
M.green-GPI
Fluorescein-GPI
(a)
Figure 4.10 (Continued)
107
0 10 20 30 40 50
30
40
50
60
70
80
90
Ha
rdn
es
s (
Hv)
Load (g)
Pure GPI
L.Prol-GPI
(b)
Figure 4.10 Load vs Hardness plot of (a) dyes and (b) amino acids doped
GPI crystals
Table 4.5 Mechanical properties of pure, dyes and amino acid doped
GPI crystals
CrystalMaximum
value of ‘Hv’(kg/mm2)
Meyer’sindex ‘n’
Stiffnessconstant
‘C11’ (MPa)
Yieldstrength ‘ y’
(MPa)
GPI 82 1.94 2234.47 27.33
R.B-GPI 100 1.88 3162.28 33.33
M.green-GPI 100 1.97 3162.28 33.33
Fluorescein -GPI 130 1.88 5004.96 43.33
L.Prol-GPI 84 1.98 2330.71 28.00
4.4 CONCLUSION
Single crystals of dyes and amino acid doped GPI crystals were
grown by solvent evaporation and temperature lowering techniques. The
108
grown crystals were subjected to various characterizations to realize the
physical properties of doped GPI materials. Single crystal XRD results reveal
the variation of cell parameters and structural morphologies of the doped
crystals with pure GPI crystal. X-ray powder diffraction method was used to
identify the crystalline phases of dyes and amino acid doped GPI crystals.
X-ray rocking curves were plotted for doped crystals using HRXRD analysis,
which reveals the crystalline perfection of crystals. FWHM of rhodamine-B,
malachite green, fluorescein and L-Proline doped GPI crystals were 56, 30, 20
and 7.5 arc sec respectively. L-Proline doped GPI crystal are nearly perfect
single crystals without having any internal structural grain boundaries. On the
other hand, grain boundaries, low angle tilt boundaries and interstitial defects
were observed for dyes doped GPI crystal specimens. The incorporation of
dyes in the pure crystalline matrix was identified by absorption of 787, 658
nm in the UV-Visible spectrum. It was also observed that the transparency of
rhodamine-B, malachite green doped crystals were decreased considerably.
Paraelectric to ferroelectric transition temperature of pure and doped GPI
crystals was determined by DSC measurement. Transition temperature (Tc)
was improved for malachite green, fluorescein and L-Proline doped crystals
where as decreased for rhodamine-B doped crystal. Piezoelectric charge
coefficient (d33) was measured for unpoled and poled samples of doped GPI
crystals. After poling there was a slight increment in d33 values for doped GPI.
P – E hysteresis loop of pure and doped GPI crystals were measured and the
ferroelectric parameters were calculated. Mechanical stabilities of pure and
doped GPI crystals were analyzed using Vicker’s microhardness analysis and
mechanical properties of crystals were calculated.