In order to clarify the relation between the dissolution mechanism of H and the defect structure in alumina-rich non-stoichiometric magnesium aluminate spinels, several compositions of single crystals were grown by using the flame fusion method and their compositional dependence of the solubility of H and that of the mass density were studied by using the IR absorption and Archimedes methods, respectively. The solubility of H increased in proportion to the square root of the water partial pressure and with the increase in the excess amount of alumina. The densities of the single crystals were slightly less than the value calculated based on the reported defect structure. The compositional dependence of the solubility of H and that of the density could be explained by the model in which the concentration of the oxide ion vacancy increased with the alumina content due to the decrease in the capability of the Mg site to accept the excess Al ion.

Defect Structure of Alumina-Rich Nonstoichiometric Magnesium Aluminate Spinel. Y.Okuyama, N.Kurita, N.Fukatsu: Solid State Ionics, 2006, 177[1-2], 59-64