ION-TRANSPORT IN SUPERIONIC CONDUCTING GLASSES

Models of the dependence of conductivity with modifier content in glasses are reviewed in this paper. It is shown that the recent 'site memory effect' model provides very good fits of experimental data by predicting a power law dependence of dc conductivity or a logarithmic dependence of activation energy of conductivity on modifier content. The consequence of the mixed alkali effect (MAE) on frequency-dependent properties is emphasized. The coupling factors (for nuclear magnetic resonance-spin lattice relaxation, n(s), and for electrical conductivity relaxation, n(sigma)) are shown to be constant and independent of composition. This may indicate that the mobile ion concentration remains practically constant when one cation is replaced by another. The MAE would then be caused by a change in the mobility of mobile ions.