On the basis of general theoretical considerations, it was shown that the fraction, cV, of vacant sites for mobile ions in glasses should be small in order to understand the peculiar behavior of the internal friction in the mixed alkali effect. For small cV, the steep fall in the conductivity in the dilute foreign alkali region could be explained by the trapping of vacancies introduced by the minority ions. A demonstrative study was made of a simple hopping model, and it was shown that it permitted the representation of both the typical behavior of the internal friction (shifts of single and mixed alkali peak positions with mixing ratio and associated changes in activation energies, changes of peak heights) and of the typical behavior of tracer diffusion coefficients (sharp drop in mobility of one type of ion by replacement with a second type of mobile ion, and associated changes in activation energies). Reasonable values of the model parameters could be estimated from measured data.

Ion Diffusion and Mechanical Losses in Mixed Alkali Glasses. P.Maass, R.Peibst: Journal of Non-Crystalline Solids, 2006, 352[42-49], 5178-87