A Synopsis on

Synthesis and Characterization of Bismuth Sodium Titanate: A Lead-Free Ferroelectric Material

Submitted in partial fulfillment of the requirements for the award of the degree

Master of Technology

In

Nano-Optoelectronics

Submitted by

Ashok Ranjan: Enrollment No-409/13

Department of Applied Physics Under the supervision of

Dr. Anil Kumar Yadav Dr. Balaji I. Birajdar

(Supervisor) (Co-Supervisor)

Assistant Professor Assistant Professor

Department of Applied Physics Special Centre for Nano Sciences

BBAU, Lucknow-226025 India JNU, New Delhi-110067 India

BABA SAHEB BHIM RAO AMBEDKAR UNIVERSITY

Raibareli Road, Lucknow, 226025 (U.P) India (A CENTRAL UNIVERSITY)

SESSION (2014-2015)

Abstract

Lead zirconate titanate (PZT) based piezo-electric materials are well known for their excellent piezo-electric

properties. However, considering the toxicity of lead and its compounds, there is a general awareness for the

development of environmental friendly lead-free materials as evidenced from the legislation passed by the

European Union in this effect. Several classes of materials are now being considered as potentially attractive

alternatives to PZTs for specific applications. In this study, Lead-free ferroelectric materials will be

synthesized using the sol-gel and solid state methods. Their advantages are: lead free material, large

piezoelectric constant, strong ferroelectric properties and large remnant polarization. These can however replace

the current industry workhorse Lead containing piezoelectric material “Lead zirconate titanate (PZT)” only if

their drawbacks are overcome. These drawbacks are: low Curie temperatures (Tc), difficulties in poling

treatments and/or low relative densities and high conductivity. With this goal in mind optimized synthesis and

characterization of Lead-free ferroelectric ceramics was carried out. Following characterization tools are used:

XRD, SEM, Measurement of Dielectric properties. Rigaku XRD will be used for the phase identifications, Zeiss

SEM equipped with LaB6 gun operated at 20 kV will be used for the surface morphology and Di-electric

properties will be measured by the LCR meter.

Synthesis and Characterization of Bismuth Sodium Titanate-A Lead

Free Ferroelectric Material

Introduction

The development of an electrical charge under the application of mechanical pressure or vice versa is referred to

as the piezoelectric effect. Low piezo-electricity is the main drawback of the natural piezoelectric materials. A major

breakthrough came the discovery of PZT and BaTiO3 in 1950s and the family of these materials exhibited very high

dielectric and piezoelectric properties. To date, PZT is one of the most widely exploited and extensively used piezoelectric

materials, having secured a permanent place in the field of material science and engineering. They are widely used as a

sensor and actuator devices, multilayered capacitors, such as hydrophones, etc. with an estimated market of tens of

billions of dollars worldwide. However lead oxide, which is a component of PZT, is highly toxic and its toxicity is further

enhanced due to its volatilization at high temperature particularly during calcination and sintering causing environmental

pollution.

There had been many attempts by researches in the past to develop alternative lead-free materials but the properties are

nowhere near to the PZT system. Basically, the lead-free systems are:

Perovskite, i.e., (Bi,Na)TiO3 (BNT), BaTiO3 (BT), KNbO3, NaTaO3, etc.

Non-perovskite, i.e., bismuth layer-structured ferroelectrics, tungsten bronze type ferroelectrics, etc. while the

perovskite are suitable for actuator and high power application, BLSF seems to be a candidate for ceramic filter

and resonator applications.

The large piezoelectric response of PZT results from two factors. Primarily, the stereo-chemical activity of the 6s2 lone

pair on the lead ion causes large structural distortions from the cubic perovskite phase that results in strong coupling

between the electronic and structural degrees of freedom. Bi-based compound have similar or larger levels of ion off

sintering than Pb-based compounds, driven by stereo chemically active 6s2 lone pairs on the Bi3+ ion. This lead to large

ferroelectric polarization [1].

Ferroelectric effect:

The ferroelectric effect is an electrical phenomenon whereby certain crystals may exhibit a spontaneous dipole

moment (which is called ferroelectric by analogy with ferromagnetic - exhibiting a permanent magnetic moment).

A ferroelectric material is a material that exhibits, over some range of temperature, a spontaneous electric polarization that

can be reversed or reoriented by application of an electric field [poling].

A necessary criterion is the requirement of an ever-present spontaneous polarization, with the requirement of reversibility

or reorientation of that spontaneous polarization being a sufficient criterion for a ferroelectric phase.

An exclusion from the definition of ferroelectrics is those materials belonging to non-polar crystal classes at all

temperatures, and in which a meta-stable polarization can be induced by an external electric field. [2]

Ferroelectricity:

Property of certain non-conducting crystals, or dielectrics, that exhibit spontaneous electric polarization

(separation of the center of positive and negative electric charge, making one side of the crystal positive and the opposite

side negative) that can be reversed in direction by the application of an appropriate electric field. Ferroelectricity is named

by analogy with ferromagnetism, which occurs in such materials as iron. Iron atoms, being tiny magnets, spontaneously

align themselves in clusters called ferromagnetic domains, which in turn can be oriented predominantly in a given

direction by the application of an external magnetic field. [2]

Ferroelectric materials:

For example, barium titanate (BaTiO3) and Rochelle salt-are composed of crystals in which the structural units are

tiny electric dipoles; that is, in each unit the centers of positive charge and of negative charge are slightly separated. In

some crystals these electric dipoles spontaneously line up in clusters called domains, and in ferroelectric crystals the

domains can be oriented predominantly in one direction by a strong external electric field. Reversing the external field

reverses the predominant orientation of the ferroelectric domains, though the switching to a new direction lags somewhat

behind the change in the external electric field. This lag of electric polarization behind the applied electric field is

ferroelectric hysteresis, named by analogy with ferromagnetic hysteresis.

Ferroelectricity ceases in a given material above a characteristic temperature, called its Curie temperature, because the

heat agitates the dipoles sufficiently to overcome the forces that spontaneously align them. [2]

Dielectric constant:

Property of an electrical insulating material (a dielectric) equal to the ratio of the capacitance of a capacitor filled

with the given material to the capacitance of an identical capacitor in a vacuum without the dielectric material. The

insertion of a dielectric between the plates of, say, a parallel-plate capacitor always increases its capacitance, or ability to

store opposite charges on each plate, compared with this ability when the plates are separated by a vacuum.

If C is the value of the capacitance of a capacitor filled with a given dielectric and C0 is the capacitance of an identical

capacitor in a vacuum, the dielectric constant, symbolized by the Greek letter kappa, κ, is simply expressed as κ = C/C0.

Dielectric constant is a number without dimensions. It denotes a large-scale property of dielectrics without specifying the

electrical behavior on the atomic scale. [2]

Electric displacement:

Auxiliary electric field or electric vector that represents that aspect of an electric field associated solely with the

presence of separated free electric charges, purposely excluding the contribution of any electric charges bound together in

neutral atoms or molecules. If electric charge is transferred between two originally uncharged parallel metal plates, one

becomes positively charged and the other negatively charged by the same amount, and an electric field exists between the

plates. If a slab of insulating material is inserted between the charged plates, the bound electric charges comprising the

internal structure of the insulation are displaced slightly, or polarized; bound negative charges (atomic electrons) shift a

fraction of an atomic diameter toward the positive plate, and bound positive charges shift very slightly toward the

negative. This shift of charge, or polarization, reduces the value of the electric field that was present before the insertion

of the insulation. The actual average value of the electric field E, therefore, has a component P that depends on the bound

polarization charges and a component D, electric displacement, which depends on the free separated charges on the plates.

The relationship among the three vectors D, E, P in the meter-kilogram-second (MKS) or SI system is: D = ε0E + P (ε0 is

a constant, the permittivity of a vacuum). In the centimeter-gram-second (CGS) system the relationship is: D = E + 4πP.

The value of the electric displacement D may be thought of as equal to the amount of free charge on one plate divided by

the area of the plate. From this point of view D is frequently called the electric flux density, or free charge surface density,

because of the close relationship between electric flux and electric charge. The dimensions of electric displacement, or

electric flux density, in the meter-kilogram-second system are charge per unit area, and the units are coulombs per square

meter. In the centimeter-gram-second system the dimensions of D are the same as those of the primary electric field E, the

units of which are dynes per electrostatic unit, or stat volts per centimeter. [2]

Electrostriction:

Property of all electrical nonconductors, or dielectrics, which manifests itself as a relatively slight change of

shape, or mechanical deformation, under the application of an electric field. Reversal of the electric field does not reverse

the direction of the deformation.

The converse piezoelectric effect occurs only in a particular class of non-conducting crystals and is characterized both by

generally a much greater deformation for a given value of the electric field and by a reversal in the direction of

deformation when the electric field is reversed. [2]

Dielectric loss:

Loss of energy that goes into heating a dielectric material in a varying electric field. For example, a capacitor

incorporated in an alternating-current circuit is alternately charged and discharged each half cycle. During the alternation

of polarity of the plates, the charges must be displaced through the dielectric first in one direction and then in the other,

and overcoming the opposition that they encounter leads to a production of heat through dielectric loss, a characteristic

that must be considered when applying capacitors to electric circuits, such as those in radio and television receivers.

Dielectric losses depend on frequency and the dielectric material. Heating through dielectric loss is widely employed

industrially for heating thermosetting glues, for drying lumber and other fibrous materials, for preheating plastics before

molding, and for fast jelling and drying of foam rubber. [2]

Applications of Ferroelectric materials:

In recent years, ferroelectric materials and thin films have attracted much attention and exhibited potential in many

important applications such as:

Dynamic random access memories (DRAMS),

Non-volatile ferroelectric random access memories micro-armours and

Infrared sensors.

At present, the ferroelectric materials suitable for these devices are Pb(Zr,Ti)O3 (PZT) systems, SrBi2Ta2O9 (SBT)

systems, Bi4Ti3O12 (BIT) systems and BaTiO3 (BT) systems that are studied with a great deal of interest. In these

ferroelectric materials, BaTi0.91(Hf0.5,Zr0.5)0.09O3 (BTHZ-9), one of the BT systems, which has several advantages such as:

An extremely low coercive field,

A high remnant polarization,

Better mechanical strength and

Small deviation in composition could have a strong potential application for ferroelectric thin film devices.

In addition, the BTHZ systems, lead and/or bismuth-free material, present a great interest both for applications in the field

of environmental protection and for fundamental studies. Therefore, the BTHZ system is expected to be one of the

attractive materials suitable for ferroelectric thin film device. [3]

BNT Structure:

BNT is one of the important lead-free piezoelectric materials with perovskite structure discovered by Smolenskii

et al. As BNT composition exhibits strong ferroelectric properties of a large remnant polarization, Pr=38µC/cm2 and high

Curie temperature, Tc=320°C, it has been considered for lead-free piezoelectric ceramics as an alternative to the widely

used lead-based piezoelectric materials. The main drawback of this material is its high conductivity, consequently giving

problems in the poling process. In addition, BNT ceramics need high sintering temperature (>1200°C) to obtain the dense

body. Thus BNT is considered to be a promising candidate for lead-free piezoelectric ceramics with balanced ferroelectric

properties. [4]

Objectives:

The objective of proposed work is to synthesize BNT using chemical method.

Compare the results with the Solid-State Route.

Characterization of sample and its properties with aim to control the composition and structure of

perovskite.

Methodology:

1. Synthesis of Ferroelectric Materials: Conventional Solid-State Method

Sol-Gel Method

2. Fabrication:

Pellets of ferroelectric material will be prepared by using hydraulic pressing machine.

Fabrication of films on various substrates using Sol-gel Spin Coater process and PLD.

3. Structural/Microstructural Characterization:

Pellets/films of these materials will be subjected to extensive structural/microstructural characterization with

particular emphasis on Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) UV, FTIR and other

techniques.

References:

1. P.K.Panda, Review: environmental friendly lead-free piezoelectric materials. Received: 20 April 2009 /

Accepted: 25 May 2009 / Published online: 7 July 2009_ The Author(s) 2009. This article is published with open

access at http://www.springerlink.com.

2. Encyclopedia Britannica: http://www.britannica.com.

3. Kenji Uchino, Ferroelectric Devices, 2nd Edition: ISBN 978-1-4398-0375-2.

4. Franco Jona and G. Shirane. Ferroelectric Crystals: ISBN 0-486-67386-3 (pbk.)

Submitted To: Submitted by:

Dr. Anil Kumar Yadav Ashok Ranjan

(Supervisor) M.Tech 3rd Semester

Assistant Professor Department of Applied Physics

Department of Applied Physics BBAU, Lucknow-226025, India

BBAU, Lucknow-226025, India

Dr. Balaji I. Birajdar

(Co-Supervisor)

Assistant Professor

Special Centre for Nano Sciences

JNU, New Delhi-110067 India