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Chapter V Dielectric Study of ……
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Dielectric studies on L-threonine monohydrochloride dihydrate single crystal
have reported by Ramesh Babu et al [34].
Various parameters affect the dielectric properties. Doping of various
impurity ions changes the dielectric and optical properties. The presences of
aqueous solution of 5-10% (NH4)2Cr2O7 causes decrease in dielectric
constant D11 and D33 and asymmetry of the electro-optic coefficient r63 of ADP
crystals [35]. Studies on the dielectric properties of potassium hydrogen
phthalate single crystals have shown that the dielectric constant and dielectric
loss increase rapidly in the vicinity of the decomposition temperature [36].
The dielectric properties of ADP type crystals were investigated using
the antiferroelectric version of extended pseudo-spin model [37]. This model
was also applied to KDP. In this model the transverse polarization induced by
proton displacement along the hydrogen bond is considered. The Hamiltonian
is based on four-sublattice version of Slater-Takagi protonic configurations
around PO4 groups, which also includes long range antiferroelectric
interaction energy.
In one study, the impedance data were obtained as a function of
frequency and temperature between 40-150 o C for ADP crystals [38]. The
frequency dependent conductivity followed Jonscher’s dynamical law with
relaxation, () = () + B n
Where, is the frequency of applied ac field and B is the constant.The
obtained value of n decreased from 1.0 to 0.25 as the temperature raised.
The electrical conductivity at low temperatures below 70 o C was attributed to
the hopping of protons m O-H-O hydrogen bonds among the vacancies. The
activation energy of migration was 0.12 eV in this extrinsic region. However,
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