Diffusion of water in lithiumβ-alumina

Water diffuses into the conduction plane of lithium $\beta$-alumina. Infrared absorption measurements of single crystals treated with ${\mathrm{H}}_2$ ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ show that, although the water concentration was homogeneous throughout the sample, most of the ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ remained near the surface. This result suggests that the oxygen in a water molecule is frequently replaced by other oxygen ions in the crystal. A diffusion mechanism which involves the dissociation of the protons from the water molecule and the jump of the oxygen ion by an interstitialcy movement into an O(5) oxygen site in the conduction plane is proposed.