This document summarizes a thesis submitted for a Master's degree in nano-optoelectronics. The thesis focuses on synthesizing and characterizing bismuth sodium titanate (BNT), a lead-free ferroelectric material. BNT is studied as an alternative to lead zirconate titanate (PZT), which is widely used but toxic. The thesis will synthesize BNT using solid-state and sol-gel methods, characterize its structure and properties, and compare the results. Characterization tools like XRD, SEM, and dielectric measurements will be used. If successful, BNT could replace PZT in applications like sensors and actuators while avoiding lead's toxicity issues.

1. 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)

2. 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.

3. 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]
.

4. 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]

5. 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]

6. 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.

7. 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]

8. 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]

9. 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.

10. 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