ABSTRACT
The description of dielectric loss and relaxation with emphasis on materials in the condensed phase is continued in this chapter. We begin with Jonscher’s universal law which is claimed to apply to all dielectric materials. Distinction is made here between dielectrics that show negligible conduction currents and those through which appreciable current flows by carrier transport. Formulas for relaxation are given by Jonscher for each case. Again, this is an empirical approach with no fundamental theory to backup the observed frequency dependence of ε* according to a power law. The relatively recent theory of Hill and Dissado, which attempts to overcome this restriction, is described in considerable detail. A dielectric may be visualized as a network of passive elements as far as the external circuit is concerned and the relaxation phenomenon analyzed by using the approach of equivalent circuits is explained. This method, also, does not provide further insight into the physical processes within the dielectric, though by a suitable choice of circuit parameters we can reasonably reproduce the shape of the loss curve. Finally, an analysis of absorption in the optical frequency range is presented both with and without electron damping effects.
