A UNIFIED MODEL FOR ION CONDUCTION IN CRYSTALS OF BETA-ALUMINA AND BETA''-ALUMINA STRUCTURE

We discuss a recently developed microscopic model for ion conduction i n crystals of the beta- and beta ''-alumina type, where the charge tra nsport is associated with the motion of certain mobile defects. Monte Carlo simulations of the model provide a good quantitative description of the mixed alkali effect based on the fact that different types of mobile ions have a different preference to become part of a mobile def ect. By taking into account the Coulomb interaction between the effect ively charged defects and the disorder present in the conduction plane , also the conductivity spectra can be understood. We further show tha t our model reproduces the non-Arrhenius behavior of the dc-conductivi ty found in Na-beta ''-alumina. (C) 1998 American Institute of Physics .