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. Durng 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 coadsorption

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).

A.Markovits, C.Minot: Journal of Physics - Conference Series, 2008, 117[1],

012021