Biju Patnaik Central Library

Thesis (Ph.D)- National Institute of Technology, Rourkela

BaTi
0.6
Zr
0.4
O
3
powder was prepared from powders containing barium
oxalate
hydrate, zirconium oxy-hydroxide and titanium dioxi
de. Barium oxalate hydrate and
zirconium oxy-hydroxide were precipitated from nitr
ate solution onto the surface of
suspended TiO
2.
Phase formation behaviour of the materials was ext
ensively studied
using XRD. BaTiO
3
(BT) and BaZrO
3
(BZ) start forming separately in the system upon
calcinations in the temperature range 600–700
o
C. BT-BZ solid solution then forms by
diffusion of BT into BZ from 1050
o
C onwards. The precursor completely transforms into
BaTi
0.6
Zr
0.4
O
3
(BTZ) at 1200
o
C for 2 hours calcinations. The activation energy o
f BT
(134 kJ mol
-1
) formation was found to be less than that of BZ (1
67.5 kJ mol
-1
) formation.
BTZ formation requires 503.6 kJ mol
-1
of energy. The sintering kinetics of the powder
was studied using thermal analyzer. The mean activa
tion energy for sintering was found
to be 550 kJ mol
-1
.
Lanthanum doped BaTi
0.6
Zr
0.4
O
3
compositions Ba
1-x
La
x
Ti
0.6[1-(5x/12)]
Zr
0.4
O
3
, Ba
1-
x
La
x
(Ti
0.6
Zr
0.4[1-(5x/8)]
)O
3
and Ba
1-x
La
x
(Ti
0.6[1-x/4]
Zr
0.4[1-x/4]
)O
3
with x = 0.005, 0.01, 0.02,
0.05 and 0.1 were synthesized. Perovskite phases we
re observed for all compositions
without existence of any secondary phases.
A gradual shift of diffraction peak to the
higher angle with increasing lanthanum percentage r
eveals the contraction of perovskite
lattice. The sintering behaviour was studied using
thermal analyzer. Sinterability of the
dielectrics decreases with increasing lanthanum sub
stitution. The frequency dependence
of dielectric permittivity and tan
δ

of the ceramics were investigated. It was found tha
t
both dielectric permittivity and tan
δ
decreases with increase in lanthanum percentage.
Room temperature permittivity of lanthanum doped di
electrics was highly stable against
change in frequency. The resistivity and current de
nsity were measured for the ceramics.
It was noticed that resistivity decreases slightly
at 0.5 atom % lanthanum substitution and
then gradually increases with increasing the concen
tration. Dielectric measurements were
carried on porous samples. It was noted that dielec
tric permittivity decreases and tan
δ
increases with increase in porosity.
The temperature dependence of dielectric permittivi
ty and tan
δ
of lanthanum
doped BaTi
0.6
Zr
0.4
O
3
samples has been investigated. The results show tha
t the phase
transition temperature T
m
shifts towards low temperature with increasing La
content. The
dielectric response of the ceramics at various freq
uencies shows a diffuse phase transition
around the transition temperature T
m
. The degree of diffuseness of the phase transition
implies the existence of a composition-induced diff
use phase transition of the ceramics
where relatively large separation between maximum o
f real and imaginary parts of
dielectric spectrum exist. The transition temperatu
re T
m
is moved toward higher
temperatures with increasing frequency. A
γ
value of 1.89 from modified Curie-Weiss
law implies diffuse phase transition behaviour of t
he ceramics and show relaxor-like
behavior with a strong frequency dispersion of the
T
m
. The ceramics obey the empirical
Vogel–Fulcher relation, which again confirms the re
laxor behavior.
.
In recent years, significant progress has been achi
eved in the development of a
class of artificial intelligent systems. This growi
ng new class of technology has been
applied successfully to a wide variety of applicati
ons. Artificial neural networks (ANNs)
are relatively new computational tools and their in
herent ability to learn and recognize
highly non-linear and complex relationships makes t
hem ideally suited in solving a wide
range of complex real-world problems. Over the last
decade chemistry became a field of
their wide application. Nevertheless, few have been
known of the application of ANN
modeling technique in inorganic ceramic materials.
The experimental results of undoped
and lanthanum doped BaTi
0.6
Zr
0.4
O
3
were analyzed by back propagation (BP) network
modeling. The combination of ANN parameters for bes
t result in modeling was
identified. The modeled values closely follow the e
xperimental values suggesting the
effectiveness of the proposed modeling and indicate
that the ANN with BPA can be used
for estimation of electrical properties of the diel
ectrics. Thus, ANN based modeling
proved to be a very useful tool in dealing with pro
blems encountered in dielectric
ceramics.