FREQUENCY-DEPENDENCE OF CONDUCTIVITY IN SUPERIONIC CONDUCTING CHALCOGENIDE GLASSES

A good understanding of phenomena related to ionic transport in glasse s is still lacking. The most recent models proposed to describe micros copic processes of ion motion in glasses are based upon the observed d ependence of conductivity on frequency. This dependence is generally d escribed by the so called 'universal' law: sigma(ac) = sigma(dc) + A o mega(s). In this work, electrical conductivity measurements on superio nically conducting chalcogenide glasses of the Ag2S-GeS2-AgI family we re performed from the microwave region (6 GHz) down to audiofrequencie s (1 kHz) in the temperature range (200-300 K). In this case, the obse rved dependence of conductivity on frequency cannot be described by th e universal law but rather by a more complex law of type: sigma(omega) = sigma(dc) + A omega(s) + B omega(s') where 0 < s < 1, s' greater th an or equal to 1. Parameters A and B are thermally activated. Whereas parameter B is weakly thermally activated, activation energy of A, E(a c), can be related to dc activation energy E(dc) by E(ac) = (1 - s)E(d c).