Defect Chemistry in Crystalline Solids

Abstract

Many of the physical properties of crystalline solids depend on the presence of native or foreign point def ects. In pure compound crystals the native defects are atoms missing from lattice sites where, according to the crystal structure, atoms should be (vacancies); atoms present at sites where atoms should not be (inter­ stitials); and atoms occupying sites normally occupied by other atoms (misplaced atoms). In addition, there may be defects in the electronic structure: quasi-free electrons in the conduction band or electrons missi ng from the valence band (holes). In impure or doped crystals there are also defects involving the foreign atoms. These may occupy normal lattice sites (substitut ional foreign atoms) or interstitial sites (interstitial foreign atoms). In elemental crystals simil ar point defects occur, only misplaced atoms are missing. Defects can be represented by symbols, atoms being represented by their normal chemical symbol, vacancies by V. Subscripts indicate the lattice site, characterized by the atom normally occupying that site. Thus VA is a vacancy at an A site. Inter­ stitial sites are indicated by a subscript i, Ai being A at an interstitial site. Electrons are represented bye, holes by h.