The hydration of this material in water vapor was investigated, for various deviations from stoichiometry and at 2 partial pressures, by measuring the weight of the specimen. It was found that the reaction was relatively insensitive to the degree of deviation from stoichiometry, but was extensive under a water vapor pressure of 2.7kPa at room temperature or 140C. This was attributed to decomposition via reaction with water. A weight gain was also detected under a water vapor pressure of 270Pa. The weight gain under lower vapor pressures was assumed to be controlled by the diffusion of OH-. The diffusion coefficients which were calculated from these measurements compared favorably with the coefficient for O diffusion.

Y.Ikuma, M.Yoshimura, S.Kabe: Journal of Materials Research, 1990, 5[1], 17-21