Abstract
Periodic DFT calculations have been used to study the creation of Schottky defects on MO2(110) rutile surface where M=Ti or M=Sn. These defects are oxygen vacancies: a bridging oxygen atom is removed from the surface creating an F°S center and readsorbed on a vicinal site. The readsorption permits to compensate a part of the energy cost required for the removal. Along this process, the stoichiometry and the atomic oxidation states remain those of the perfect surface. The energy cost for such defect is found almost 5 times weaker for TiO2(110) than for SnO2(110). Next, we analyze the effect of hydrogen coadsorption. We start considering the hydrogenated surface, one hydrogen atom binding to a bridging oxygen atom and reducing the metal-oxide surface. The Schottky process then becomes the displacement of a hydroxyl ion which desorbs and readsorbs on surface titanium just as basic species do. This coadsorption does not affect the energy cost in the case of TiO2, while, in the case of SnO2(110), it makes it weaker. This decrease in mainly due to the magnitude of the interaction between a hydroxyl group and the Sn4+ surface atom, that is large compared with that for O.
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