Studies of the equilibrium behaviour of crystalline fast-ionically conducting systems

Abstract

Investigations of several different beta- and beta″-aluminas have found that cationic ordering phenomena play a major role in determining the properties of many of these systems. Low-temperature equilibrium states in the “single-ion” isomorphs of the beta″-aluminas are only attained by careful annealing treatments or by slow cooling the samples from the temperature of ion exchange. Rapidly cooled crystals contain non-equilibrium disordered arrangements that are responsible for the high ionic conductivity. In “mixed-ion” systems ordering between the different cations also inhibits the ionic conductivity. Beta″-aluminas containing two ions of different valence can form cationic arrangements involving substantial long-range correlations.