Structural characteristics and non-stoichiometry of β-alumina type compounds

Structural characteristics of β-alumina type compounds are investigated by comparing them with those of isomorphous compounds in the BaOFe₂O₃MeO system (where Me represents a spinel-forming divalent ion) and by observing the lattice images of a series of β-alumina type compounds by transmission electron microscopy. The results suggest that the stoichiometry of β-alumina is fixed but is far from the idealized formula Na₂O·11Al₂O₃ and that the existence of the solubility range is due to its structural characteristics to accommodate mixed periods in the structure rather than to a change in the Na composition in the “defect” layer. Important consequences derived from these conclusions are discussed.