Analysis of electrical relaxation in ionically conducting glasses and melts

The Havriliak-Negami (HN) relaxation function was used to analyze electric field relaxation data for a model Li2O-Al2O3-2SiO(2) glass. The HN function gave an excellent description of the frequency dependence of the imaginary part of the electric modulus M '' in the intermediate frequency range (10(-2) less than or equal to omega[tau] less than or equal to 10(2)). However, at low frequencies the HN function predicted unphysical behavior, i.e., it failed to predict the levelling off of the real parts;of the complex conductivity, sigma', and of the complex permittivity, epsilon', at static low frequency values. It appears that, for fits using a minimal number of adjustable parameters, the distribution of relaxation times associated with the KWW or stretched exponential relaxation function, phi(t) = exp(-t/tau(KWW))(beta), continues to give the best description of electrical relaxation in materials containing large concentrations of mobile ions.