Mixed-alkali effect: some new results

Most aspects of the mixed-alkali effect (MAE) are shown to be consistent wi th calculations employing critical rate analysis to hopping conduction in a random energy landscape. The temperature and frequency dependence of the c onductivity can be understood when four factors are incorporated into theor etical models. These four factors are: existence of a spread of barrier hei ghts and well depths, applicability of critical rate analysis, independence of low-lying energy states of different alkali ions, and relevance of dyna mic Coulomb interactions. New calculations of the ac conductivity at lower frequencies, but still above the loss peak frequency of the dielectric rela xation, are given. Such frequencies are low enough to allow more quantitati ve comparison with experimental results for the stretching parameter descri bing stretched exponential relaxation. This comparison provides additional support for the theoretical interpretation. (C) 1999 Elsevier Science B.V. All rights reserved.