Download (4Mb) - Etheses - Saurashtra University

Chapter V Dielectric Study of ……
-
Physically, one may consider the dipole moments as trying to line up,
but jostled by their thermal motion and not all of them are successful. Since
the energy of dipole in an electric field E is given by
angle (dΩ) is
U = - E Cos (5.9)
According to statistical mechanics, the number of dipoles in a solid
= 2 Sin exp (μE Cos/kT) (5.10)
Hence the average dipole moment is given as
= Net number of the assembly / Total number of dipoles
Integrating in the interval of 0 to , one yields
= L(a) = Cot ha - l/a (5.11)
0
Where, L(a) is called the Langevin function [4] and
194
(5.12)
If a is small, which is true under the quite wide conditions, equation
(5.12) may be approximated by, = (5.13)
i.e., the polarizability is inversely proportional to the absolute temperature.
(iv) Space charge Polarization:
Space charge polarization is important in dielectric materials, which
contain charge carriers that can migrate for some distance through the bulk of
the material (via, e.g., diffusion, fast ionic conduction, or intercalation) thus
creating a microscopic field distortion. Such a distortion appears to an outside
observer as increase in capacitance of the sample and may be
distinguishable from real rise of the dielectric permittivity. Space charge
polarization is the only type of electrical polarization that is accompanied by a