Biomedical Engineering Reference
In-Depth Information
E
σ
= 0.07eV
-5.8
-6.0
-6.2
2.0
2.2
2.4
2.6
10
3
/T (K
-1
)
Figure 14.6
Temperature dependence of σ
dc
for present material.
E
kT
exp
(14.2)
dc
0
B
with activation energy E
σ
= 0.07eV, as shown in Figure 14.6. h e circles
in this i gure are the experimental points and the solid line is the least-
squares straight line i t.
In Figure 14.7 is shown the variation of
and with temperature at var-
ious frequencies. At temperature far above T
m
at two frequencies (100 Hz
and 1 KHz), a monotonous increase in the value of caused by electrical
conduction is observed. h e phase transition involved is dif use and dielec-
tric constant is markedly dispersive below the temperature T
m
'
at which it
peaks. h e temperature T
m
'
and T
m
”
corresponding to the peaks in real ( )
and imaginary ( ) parts of the dielectric constant are not coincident and
this is a typical characteristic of a relaxor. In fact, T
m
”
is less than T
m
'
and the
temperatures T
m
'
and T
m
”
are frequency dependent and they increase with
increasing frequency.
Figure 14.8 again shows the dependence of with temperature for dif-
ferent frequencies at close interval. A rapid rise of ε with temperature in
the lower-frequency range as shown in this i gure is due to space-charge
polarization. A similar kind of result has also been obtained by Raevski
et
al.
[10] for a non-lead system like Sr Fe
1/2
Nb
1/2
O
3
.
h e angular frequency ω (=2πυ) dependence plots of the real ( ) part
of the complex dielectric permittivity (ε*) and the dielectric loss tangent
(tan δ) of present material at several temperatures between 303 K and
483 K are plotted in Figure 14.9. A relaxation is observed in the entire
