Models for the dependence of the conductivity upon the modifier content of such glasses were reviewed. It was shown that a new so-called site-memory model provided a very good fit to experimental data by predicting a power-law dependence of the direct-current conductivity, or of the logarithmic dependence of the activation energy for conductivity, upon the modifier content. The influence of the mixed-alkali effect upon the frequency-dependent properties was emphasized. The coupling factors for nuclear magnetic resonance-spin lattice relaxation and electrical conductivity relaxation were shown to be constant, and independent of the composition. This was suggested to indicate that the mobile ion concentration remained essentially constant when one cation was replaced by another. The mixed-alkali effect was then expected to be caused by a change in the mobility of the mobile ions.

A.Pradel, M.Ribes: Journal of Non-Crystalline Solids, 1994, 172-174, 1315-23