Oxide surface defects and the reactivity of surfaces

The most prevalent type of point defect that occurs at metal oxide surfaces is an oxygen vacancy (Henrich, 1983, 1985), and this is illustrated for MgO(lOO) and TiOjlllO) in Figs. 8.13 and 8.16. At such defects, there is a reduction of the ligand coordination of adjacent surface cations, generally from five to four. Removal of an oxygen anion also reduces the 

This defect level located near the conduction band is very important because of its high chemical activity. Experimentally, it has been established that the photocatalytic activity of the rutile surface increases greatly when reduced (oxygen deficient) compared to the clean surface (Mavroides et al., 1975). Defect sites on all oxide surfaces are usually very active for adsorption, whereas the nearly perfect surfaces of oxides where the cation is in its highest oxidation state are generally inert (Flen-rich, 1987). 

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