Hydroxylation of the surface of the corundum basal plane

We report theoretical investigations on the effects of hydroxylation of the basal-plane surface of corundum. Performing energy minimisation calculations at 0 K we find very small relaxations when hydroxylating the polar oxygen-terminated cut. This is in sharp contrast with the very large relaxations found for the clean, non-polar Al-terminated cut. In order to establish the stability of the hydroxylated surface, the reaction enthalpy for desorption of water from the surface has been calculated using an embedded cluster model. Since the hydroxylated surface does not contain any low-coordinated Al ions, in contrast to the clean surface, the existence of low-coordinated surface Al ions can be used experimentally to distinguish between the two cases.