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Chapter V Dielectric Study of ……
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at temperature from 70 to 79 o C, additional defects were created by breaking
the stronger hydrogen bond in ammonium groups. At temperature above 97
o C, ammonium ions in the crystal were proposed to have contributed for the
electrical conduction.
Recently, Ambujan [39] studied the effect of cation doping (Mg +2 , Cu +2 ,
Ni +2 and Ca +2 ) in KDP crystals on their dielectric properties. The variation of
dielectric constant with frequency suggested that as the frequency increased
the dielectric constant decreased and at high frequency the leveling of the plot
to the X-axis was observed. The pure KDP crystals exhibited the least values
of dielectric constant. It was observed that due to change in the sizes of the
metal dopant ions, there was change in the value of dielectric constant at any
particular frequency. The polarizability was expected to increase as the ions
were smaller and highly charged. Ambujan [39] could observe the increase in
the value of dielectric constant of doped sample in accordance with the ionic
radii of the metallic dopant.
KDP crystallizes in tetragonal crystal system with space group 14 2d.
The crystal structure consists of PO4 tetrahedral joined by four hydrogen
bonds to neighboring PO4 tetrahedral in such a way that each PO4 tetrahedral
has two hydrogen atoms associated with it giving (H2PO4) - ion. The PO4 group
and K + ions are built up in such a way that K and P atoms alternate each
other at a distance of c/2 along the c-axis. During the metal ion substitution
the hydrogen bond in the structure break down giving rise to the loosening of
the hydrogen and the creation of additional charged defects. These lattice
defects cause the increased space charge contribution.
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