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Chapter V Dielectric Study of ……
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and doubly occupied hydrogen bonds (D-defects). Other possible defects are
vacancies and defect associates [43]. The temperature dependence of
conductivity has lead Meena and Mahadevan [42] to consider that the
conductivity of KDP crystals can be determined by both thermally generated
L-defects and the foreign impurities incorporated into the lattice and
generating the L-defects there Lokshin [45] assumed that (HPO4) -2 ions are
also responsible for the formation of vacant hydrogen bonds (L-defects).
Therefore, it is easy to understand from this discussion that the proton
transport depends on the generation of L-defects. The increase of conductivity
with increase in temperature for L-histidine doped KDP and ADP crystals [42]
can be due to the interstices which are expected to be occupied by L-histidine
molecules in KDP. This induces bulk defect states due to competition in
getting the sites for the L-histidine molecules to occupy. The L-histidine
molecules can be added to some extent in addition to the replacement of ions
in the KDP and ADP lattice and creating additional hydrogen bonds. As the
conduction in KDP and ADP occurs through protons and mainly due to the
anions (H2PO4) - ions and not due to the cations (K + , NH4 + ), the additional
hydrogen bonds created may reduce the L-defects and consequently obstruct
the movement of protons. This is the possible explanation given by Meena
and Mahadevan [42] for the decrease in the conductivity value with increase
in impurity concentration. The addition of L-histidine leads to decrease
electrical parameters such as σdc, σac, εr and tanδ for both KDP and ADP
crystals, which has lead Meena and Mahadevan [42] to conclude that L-
histidine addition makes possible for the KDP and ADP crystals to become
low εr value dielectrics. Moreover, the dielectric study of amino acids (L-
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