Ordered point defects and superstructures

There is increasing experimental evidence for the superlattice ordering of vacant sites or interstitial atoms as a result of interactions between them. Superlattice ordering of point defects has been found in metal halides, oxides, sulphides, carbides and other systems, and the relation between such ordering and nonstoichiometry has been reviewed extensively (Anderson, 1974, 1984 Anderson Tilley, 1974). Superlattice ordering of point defects is also found in alloys and in some intermetallic compounds (Gleiter, 1983). We shall examine the features of some typical systems to illustrate this phenomenon, which has minimized the relevance of isolated point defects in many of the chemically interesting solids. 

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Isolated, random point defects and valence defects Defect pair association Rearrangement of coordination environment in isolated defect clusters or microdomains 1- or 2-dimensional assays of ordered defects or reorganized defect complexes Fully defined superstructures or shear structures... 

Point defects are vacancies, interstitials, antisites and impurities. The first three of these are intrinsic defects while impurities are extrinsic. Antisite defects only occur in a lattice with a superstructure order. 

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