Study Of Structural, Electrical And Optical Properties Of Lead-Free (Bi0.5na0.5)Tio3 Based Ceramic Systems

By: Parija, BishwanathanContributor(s): Panigrahi, S [Supervisor] | Department of PhysicsMaterial type: TextTextLanguage: English Publisher: 2012Description: 233 pSubject(s): Physics | Nuclear PhysicsOnline resources: Click here to access online Dissertation note: Thesis (Ph.D)- National Institute of Technology, Rourkela Summary: In view of the processing and environmental issues pertaining to lead-based ferroelectric materials, investigations on lead-free ferroelectrics are carried intensively in recent years. These materials are interesting because they are flexible with respect to structural changes and functional properties. This study focuses on a lead-free, high temperature ceramic capacitor material having the base composition of (Bi0.5Na0.5)TiO3. The goal is to modify this base composition to create a material that has diffuse-phase-like dielectric behaviour, while maintaining its inherently good high temperature dielectric properties. This will alleviate some circuit design problems, and will create a component that is less susceptible to drastic environmental changes. Areas of interest include aerospace and weapons system applications, motor control, geological down-hole-drilling equipment and many more. An extensive experimental compositional matrix, along with theoretical modelling, has been investigated to modify the base material to attain the goals set forth. (Bi0.5Na0.5)TiO3, SrTiO3, BaTiO3 and Ba(Zr0.25Ti0.75)O3 ceramics were successfully calcined by two stapes conventional solid-state reaction method. The solid-solutions of (1- x)(Bi0.5Na0.5)TiO3-xSrTiO3, (1-x)(Bi0.5Na0.5)TiO3-xBaTiO3 and (1-x)(Bi0.5Na0.5)TiO3- xBa(Zr0.25Ti0.75)O3 with concentrations 0 ≤ x ≤ 0.08 were prepared successfully by conventional solid-state reaction route. The optimized sintering temperature is found to be 11500C for 4 hrs. The X-ray diffraction study shows that all the compositions are having a single phase perovskite structure which confirms that a complete solid-solution is formed. The lattice parameter and cell volume decreases with increase in solid solution. A morphotropic phase boundary (MPB) exists in (1-x)(Bi0.5Na0.5)TiO3-xBaTiO3 at x = 0.07 and in (1-x)(Bi0.5Na0.5)TiO3-xBa(Zr0.25Ti0.75)O3 at x = 0.05. The same thing is also observed in Raman spectroscopy. The microstructure of all samples shows a change of shape from rectangular to quasi-spherical with decrease in grain size. High dense and smaller grain iv size has affected the conductivity and electromechanical property to achieve a higher value of d33 and kp as well as enhanced the ferroelectric behavior in MPB compositions. The temperature-dependent dielectric study shows increases in dielectric constant in all compositions whereas in (1-x)(Bi0.5Na0.5)TiO3-xBaTiO3 and (1-x)(Bi0.5Na0.5)TiO3-x Ba(Zr0.25Ti0.75)O3, increases upto morphotropic phase boundary (MPB) and then decreases with further increase in solid solution. Also, the temperature-dependence of dielectric measurement reveals that the solid-solutions experience two phase transitions from ferroelectric to anti-ferroelectric and from anti-ferroelectric to paraelectric. The dielectric loss decreases with the increase in solid-solution content in the high temperature region. The diffusivity of the ceramics increases with higher content of solid-solution implying that the solid-solution introduces defects and localized strain field. The impedance spectroscopy study of all compositions shows a dielectric relaxation of non-Debye type and the relaxation frequency shifted to higher frequency side with the increase of temperature and lower frequency side with the increasing concentrations. In (Bi0.5Na0.5)TiO3, (1-x)(Bi0.5Na0.5)TiO3-xSrTiO3 and (1-x)(Bi0.5Na0.5)TiO3-xBaTiO3, only grain effect is observed indicating the uniform distribution and homogeneity in the specimen under study, whereas in (1-x)(Bi0.5Na0.5)TiO3-xBa(Zr0.25Ti0.75)O3, grain and grain boundary effect is observed in the Cole-Cole plot above the temperature 4300C. The relaxation phenomenon is found to exist due to oxygen vacancies. The activation energy obtained from the impedance, modulus and conductivity data, increases with increasing of solid-solution content. The electrical conductivity studies showed the negative temperature coefficient of resistance (NTCR) character. The optical study shows the variation of optical band gap energy (Egap) in (1-x)(Bi0.5Na0.5)TiO3-xBaTiO3 and (1-x)(Bi0.5Na0.5)TiO3- xBa(Zr0.25Ti0.75)O3 solid-solutions.
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Thesis (Ph.D)- National Institute of Technology, Rourkela

In view of the processing and environmental issues pertaining to lead-based ferroelectric
materials, investigations on lead-free ferroelectrics are carried intensively in recent years.
These materials are interesting because they are flexible with respect to structural changes
and functional properties. This study focuses on a lead-free, high temperature ceramic
capacitor material having the base composition of (Bi0.5Na0.5)TiO3. The goal is to modify
this base composition to create a material that has diffuse-phase-like dielectric behaviour,
while maintaining its inherently good high temperature dielectric properties. This will
alleviate some circuit design problems, and will create a component that is less susceptible
to drastic environmental changes. Areas of interest include aerospace and weapons system
applications, motor control, geological down-hole-drilling equipment and many more. An
extensive experimental compositional matrix, along with theoretical modelling, has been
investigated to modify the base material to attain the goals set forth.
(Bi0.5Na0.5)TiO3, SrTiO3, BaTiO3 and Ba(Zr0.25Ti0.75)O3 ceramics were successfully
calcined by two stapes conventional solid-state reaction method. The solid-solutions of (1-
x)(Bi0.5Na0.5)TiO3-xSrTiO3, (1-x)(Bi0.5Na0.5)TiO3-xBaTiO3 and (1-x)(Bi0.5Na0.5)TiO3-
xBa(Zr0.25Ti0.75)O3 with concentrations 0 ≤ x ≤ 0.08 were prepared successfully by
conventional solid-state reaction route. The optimized sintering temperature is found to be
11500C for 4 hrs. The X-ray diffraction study shows that all the compositions are having a
single phase perovskite structure which confirms that a complete solid-solution is formed.
The lattice parameter and cell volume decreases with increase in solid solution. A
morphotropic phase boundary (MPB) exists in (1-x)(Bi0.5Na0.5)TiO3-xBaTiO3 at x = 0.07
and in (1-x)(Bi0.5Na0.5)TiO3-xBa(Zr0.25Ti0.75)O3 at x = 0.05. The same thing is also observed
in Raman spectroscopy. The microstructure of all samples shows a change of shape from
rectangular to quasi-spherical with decrease in grain size. High dense and smaller grain
iv
size has affected the conductivity and electromechanical property to achieve a higher value
of d33 and kp as well as enhanced the ferroelectric behavior in MPB compositions.
The temperature-dependent dielectric study shows increases in dielectric constant in all
compositions whereas in (1-x)(Bi0.5Na0.5)TiO3-xBaTiO3 and (1-x)(Bi0.5Na0.5)TiO3-x
Ba(Zr0.25Ti0.75)O3, increases upto morphotropic phase boundary (MPB) and then decreases
with further increase in solid solution. Also, the temperature-dependence of dielectric
measurement reveals that the solid-solutions experience two phase transitions from
ferroelectric to anti-ferroelectric and from anti-ferroelectric to paraelectric. The dielectric
loss decreases with the increase in solid-solution content in the high temperature region.
The diffusivity of the ceramics increases with higher content of solid-solution implying
that the solid-solution introduces defects and localized strain field.
The impedance spectroscopy study of all compositions shows a dielectric relaxation of
non-Debye type and the relaxation frequency shifted to higher frequency side with the
increase of temperature and lower frequency side with the increasing concentrations. In
(Bi0.5Na0.5)TiO3, (1-x)(Bi0.5Na0.5)TiO3-xSrTiO3 and (1-x)(Bi0.5Na0.5)TiO3-xBaTiO3, only
grain effect is observed indicating the uniform distribution and homogeneity in the
specimen under study, whereas in (1-x)(Bi0.5Na0.5)TiO3-xBa(Zr0.25Ti0.75)O3, grain and grain
boundary effect is observed in the Cole-Cole plot above the temperature 4300C. The
relaxation phenomenon is found to exist due to oxygen vacancies. The activation energy
obtained from the impedance, modulus and conductivity data, increases with increasing of
solid-solution content. The electrical conductivity studies showed the negative temperature
coefficient of resistance (NTCR) character. The optical study shows the variation of optical
band gap energy (Egap) in (1-x)(Bi0.5Na0.5)TiO3-xBaTiO3 and (1-x)(Bi0.5Na0.5)TiO3-
xBa(Zr0.25Ti0.75)O3 solid-solutions.

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