On the defect structure in nonstoichiometric metal oxides

Abstract

A number of important physical and chemical properties of nonstoichiometric transition metal oxides are influenced by kind and concentration of defects in the crystalline lattice of these materials. Until quite recently it was thought that the relation between the nature of defects in the lattice of these oxides and their physical and chemical properties could be explained satisfactorily based on point defect theory. Today it is known that such an approach is correct only in the case of very small defect concentrations. At higher concentrations the mutual interaction between point defects results in formation of complexes and defect clusters called extended defects. These extended defects can become further ordered, which leads to superstructure ordering and to formation of intermediate phases. In some cases point defects can become eliminated in the process of crystallographic shear which is connected with formation of a whole series of intermediate phases.