Structural studies of highly non-stoichiometric polycrystalline sodium and silver beta-aluminas

Highly non-stoichiometric (x approximately 0.45) sodium and silver beta-aluminas have been studied by powder neutron diffraction. Results on the sodium material confirm the defect mechanism previously observed in materials with a lower degree of non-stoichiometry but accurate sodium occupations in the mirror plane could not be obtained. In contrast, for the silver beta-alumina prepared by ion exchange, the silver ion distribution could be satisfactorily refined. The stable site in stoichiometric silver beta-alumina is no longer occupied. (Auth.)