The dynamics of ions in glasses: importance of ion–ion interactions

We present frequency dispersion of two oxide glasses with widely different ion concentrations to show that ion–ion interaction and correlation plays an important role in determining the dc conductivity and the low frequency cooperative part of the dispersion. The origin of the near constant loss, which always appears at higher frequencies/lower temperatures, is traced to few and infrequent independent jumps of the ions out of their cages without the effect of ion–ion correlation. The coupling model gives quantitative support to this interpretation of the entire dispersion. The largest effect of the mixed alkali effect in glasses occurs in the dilute foreign-alkali region, where one foreign alkali immobilizes a large number of host ions. Results show that this feature of the mixed alkali effect can only be explained if ion–ion interaction/correlation is included in the description of the ion dynamics.