Download (4Mb) - Etheses - Saurashtra University

Chapter V Dielectric Study of ……
-
displacement of the electrons in the direction of applied field, which in turn
gives rise to polarization. It is the displacement of electrons with respect to the
atomic nuclei. To be more precise the displacement of electrons, under the
action of external electric field, the electronic orbits occurs around the atomic
nuclei. When the external electric field is superposed, this type of polarization
occurs during a very brief interval of time (order of 10 -15 sec) i.e. the time of the
period of oscillations of ultraviolet rays [1].
(ii) Ionic Polarization
It is the mutual displacement of ions forming hetro-polar (ionic)
molecule. A short time is required for the process of ionic polarization to set in
but longer than for electronic polarization i.e. 10 -12 to10 -13 sec.
The bonds between atoms are stretched by applied electric fields when
the lattice ions are charged. This is easily visualized with an alkali halide
crystal in figure (5.5), where small deformation of the ionic bond will occur
when a field is applied, increasing the dipole moment of the lattice.
Figure: 5.5 Stretching of Alkalihallide bonds when ion is charged.
Altogether, the processes of electronic and ionic polarizations have
much in common. Both phenomena may be regarded as the varieties of
polarizations caused by the deformation which is displacement.
(iii) Orientational Polarization
The polar dielectrics exhibit tendency towards orientational polarization.
According to Debye [3], this type of polarization is due to the rotation or
192