Structure and transport in non-stoichiometric β Al2O3

Presents results of a detailed theoretical survey of the defect structure and transport properties of non-stoichiometric beta Al 2 O 3 . The authors methods are based on a generalised mott-Littleton approach which includes a full explicit treatment of lattice relaxation around defect species. Their calculations show that the anti-Beevers-Ross site is the stable configuration for excess Na + ions. These migrate by an interstitialcy mechanism. In grossly nonstoichiometric beta Al 2 O 3 , however, the migration mechanism may more closely resemble the vacancy mechanism operative in beta "Al 2 O 3 . The authors' results account for the observed differences between the conductivities of the stoichiometric and non-stoichiometric phases. They differ considerably from those of earlier theoretical studies of Wang et al. (1975); this is attributed to improvements in the interatomic potentials and the inclusion of lattice relaxation in the authors study.