Abstract
Infrared absorption studies have been carried out on the vibrations of sodium ions in the mirror plane of both non-stoichiometric and nearly stoichiometric sodium beta -alumina. Absorption by the mixed crystals Nax(NH4)1-x beta -alumina has also been measured for 0-1. The results are related to configurations of sodium ions in the mirror plane and they are used in conjunction with recent calculations by Walker and Catlow (1982) to discuss models for ionic conduction.