FREQUENCY-DEPENDENT IONIC-CONDUCTIVITY IN AGI-AGPO3 GLASSES

Ac conductivity measurements have been performed on the superionic gla ssy system (AgI)(x)(AgPO3)(1-x). It is found that there are two contri butions to the ac conductivity: one, dominant at high temperatures/low frequencies, is characterised by a sublinear frequency exponent of th e conductivity, s(1) similar or equal to 0.5, and the conductivity is thermally activated, with an activation energy smaller than, but compa rable to, that of the dc conductivity; the second, dominant at low tem peratures/high frequencies, is characterised by a superlinear frequenc y exponent, s(2) similar or equal to 1.2, and the conductivity is also thermally activated, but the activation energy is an order of magnitu de smaller. The former behaviour is interpreted in terms of the diffus ion-controlled relaxation model, and the latter in terms of local ioni c hopping motion within a double-well potential with an exponentially decreasing distribution of barrier heights.