FREQUENCY-DEPENDENT CONDUCTIVITY IN IONICALLY AND ELECTRONICALLY CONDUCTING AMORPHOUS SOLIDS

A review is given of the experimental data pertaining to the frequency -dependent (ac) conductivity characteristic of ionically, and electron ically, conducting amorphous solids. It is found that, although at fir st sight the ac behaviour appears to be universal, substantial differe nces exist between the ac response exhibited by these two classes of n on-crystalline material, particularly concerning the temperature depen dence of the ac conductivity. The various models that have been propos ed to account for this behaviour are summarized, and the probable mech anisms of charge transport responsible for the experimentally observed frequency-dependent conductivity in amorphous solids are emphasized.