Biju Patnaik Central Library

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 respec
t to structural changes and functional properties. These materials have
potential device applications such as capacitors, sensors, actuators, and memory
storage and microwave devices. This thesis is an attempt to elucidate the effect of
substitution of het
erovalent ions (Bi, Y, Dy) on the
‘
A
’
site of
Barium Zirconium
Titanate BaZr
0.25
Ti
0.75
O
3
(BZT)
pervoskite
. Their
structural, morphological, electrical
and optical properties are investigated.
The XRD study on the ceramic compositions
showed single phase cu
bic perovsite structure at room temperature.
The existence
of Raman active modes
in
BaZr
0.25
Ti
0.75
O
3
is associated with the structural order
-
disorder at short
-
range into the lattice due to the presence of polar [TiO
6
] distorted
clusters
. The SEM micrograph shows that the grains are uniformly distributed
throughout the surface and the average grain size
decreases with
substitution
heterovalent ion doping in
BaZr
0.25
Ti
0.75
O
3
ceramic.
The dielectric study confirmed
the relaxor nature of the
heterovalent ions
doped ceramic and the transition
temperature (T
m
), dielectric permittivity and dielectric loss are decreasing with
iv
increase in
heterovalent ions
concentration .The diffusivity of ceramics increases
with increase in
heterovalent ions
concentration. The impedance and modulus
spectroscopy were employed to evaluate the different electrical properties of the
grain and grain boundary of the ceramics. The optical band gaps were calculated
from UV
–
Visible spectroscopy ceramic suggested the
presence of intermediary
energy levels within the band gap. The Photo luminescent study of
heterovalent ions
doped BaZr
0.25
Ti
0.75
O
3
, when excited with 350 nm wavelength at room temperature,
exhibited broad PL band with a maximum emission in blue region.