Download (4Mb) - Etheses - Saurashtra University

Chapter V Dielectric Study of ……
-
glutamic acid, L-histidine and L-valine) doped KDP crystals was carried out by
Kumaresan and Kumaresan [46, 47]. The authors found that on doping of
amino acids the value of dielectric constant of KDP crystals decreased and
also decreased with increase in the frequency of applied field. Moreover, L-
arginine, L-histidine and glycine doped KDP crystals were grown by Kumar
and Babu [48]. They have studied the dielectric behavior and found the
dielectric constant and dielectric loss less in doped crystals in compare to
pure KDP crystals.
Udupa et al [49] have found for KDP crystals that the dielectric
constant decreases with the increase of temperature at all frequencies
studied. The same authors also have observed the appreciable increase in
the value of dielectric constant after impurity (MgO) addition and decrease in
its value with increase in frequency.
An anomalous dielectric behavior in ferroelectric KDP was
noticed by Gilchrist [50]. The dielectric permittivity ε = ε’ – ε” of KDP pressed
powder was measured between temperature from 1.4 K to 25 K in the
presence of d.c. electric field bias. Usually, if the bias was switched at time t =
0, the ε’ and ε” would jump to new values and then decrease approximately as
log t (6 < t < 20000 S). This well-know effect, which is also found in single
crystals, can be attributed to the switchable micro-domains present
accidentally in crystals but present more in powders. A very different type of
after effect was observed in a narrow temperature range from 7 K to 8 K. The
ε’ jumped to lower value, thereafter increased with t according to a stretched
exponential with a temperature dependent time constant. This is similar to the
extrapolation of the Arrhenius law of known but unassigned weak-field
209