MIXED-ALKALI EFFECT IN CRYSTALS OF BETA-ALUMINA AND BETA''-ALUMINA STRUCTURE

We develop a microscopic model for the mixed alkali effect in crystals of the beta- and beta ''-alumina type, which is based on the formatio n of certain mobile defects and the fact that different types of mobil e ions have a different preference to become part of these defects. Ou r computer simulations for the ionic conductivity are in excellent agr eement with experimental data. Our model predicts a common shape of th e rescaled conductivity isotherms independent of temperature and the s pecific type of probe, which is also in agreement with the available e xperimental results.