Towards a universal behaviour of ion dynamics in Na- and Rb-oxide glasses

Activation enthalpies of ionic conductivities in Na–Rb alumino-germanate and borate glasses are reviewed. Correlations between the activation enthalpy and the ratio of average distances between like alkali ions, 〈dion〉, to the average distances between network–former atoms, 〈dnetwork〉, are elucidated for single- and mixed-alkali glasses. The Haven ratio is shown to decrease with decreasing 〈dion〉/〈dnetwork〉. Interstitial-like and substitutional-like subnetworks of ion sites are suggested. The experimentally observed dependence of the Haven ratio on 〈dion〉/〈dnetwork〉 is consistently reproduced by a Monte Carlo simulation of ion dynamics on this random network including single and collective ion jumps.