ABSTRACT
The presence of defects strongly influences the electrical, optical, adsorptive, and catalytic properties of the oxides. It also controls transport phenomena in solids. Here we shall discuss only the most important features of the defect state in the oxides and simple oxygen-oxide equilibria which determine the deviations from stoichiometry. However, it should be noticed that point defects can also be present in stoichiometric oxides. In a stoichiometric oxide MO two kinds of such defects are of special interest: the Schottky and the Frenkel defects. Schottky defects can be described as the result of migration of a cation-anion pair to the surface, leaving behind in the bulk a pair of cation and anion vacancies V& and Vo
MO ~ V~ + Vo (3.15)
Both vacancies bear formal charges: the cationic one 2-and the anionic one 2+.
