Periodic DFT calculations were used to study the creation of Schottky defects on MO2(110) rutile surface where M = Ti or Sn. These defects were oxygen vacancies: a bridging oxygen atom was removed from the surface creating an F°S center and re-adsorbed on a vicinal site. The re-adsorption permitted compensation of a part of the energy cost required for the removal. During this process, the stoichiometry and the atomic oxidation states remained those of the perfect surface. The energy cost for such a defect was found to be almost 5 times lower for TiO2(110) than for SnO2(110). The effect of hydrogen co-adsorption was then analyzed. The hydrogenated surface was considered to involve one hydrogen atom binding to a bridging oxygen atom and reducing the metal-oxide surface. The Schottky process then became the displacement of a hydroxyl ion which desorbed and re-adsorbed on surface titanium just as the basic species did. This co-adsorption did not affect the energy cost in the case of TiO2 while, in the case of SnO2(110), it made it weaker. This decrease was due mainly to the magnitude of the interaction between a hydroxyl group and the Sn4+ surface atom, that was large compared with that for O.

Comparative Creation of Surface Schottky Defects on SnO2(110) and TiO2(110). Markovits, A., Minot, C.: Journal of Physics - Conference Series, 2008, 117[1], 012021