Biomedical Engineering Reference
In-Depth Information
13.4.2.3
Some of the Results on BiFeO3 and Its Substituted
Compounds
h e temperature dependence of dc electrical conductivity (σ
dc
) for pure
and La-substituted BiFeO
3
compound has been evaluated by taking the
steady-state values of current, and the results are plotted for elevated tem-
perature range from 323 K to 667 K, as shown in Figure 13.21. Below the
temperature of around 465 K, the conductivity of all the samples is too low
to be measured. At er 465 K, the conductivity of all the samples increase
up to the measured temperature range. h e increase in conductivity may
be explained by the fact that it is a consequence of thermally activated pro-
cesses, which can be described by the Arrhenius relation:
σ = σ
o
exp (-Ea/k
β
T)
(13.9)
where σ
o
is the pre-exponential factor, k
β
is the Boltzmann constant and its
value is 8.6 x 10
-5
eV/K, and Ea is the activation energy.
In insulators/dielectrics, there is an energy gap between the valence and
conduction bands, so energy is needed to promote an electron from valence
band to conduction band. h is energy is known as activation energy (Ea)
and it may come from heat, because the electrons can not reach the conduc-
tion band at ordinary temperatures. h e activation energy of the pure sample
calculated from the slope of the log σ versus 1000/T curve is 0.814 eV which
is much higher than that obtained by Jun
et al.
[99]. h is suggests that the
x=0.0
x=0.1
x=0.2
x=0.3
x=0.4
x=0.5
-6
-7
-8
-9
-10
1.5
2.0
2.5
3.0
1000/T (K
-1
)
Figure 13.21
log σ vs 1000/T curve for Bi
1-x
La
x
FeO
3
, (x=0.0, 0.1, 0.2, 0.3, 0.4 & 0.5).
