Point defects

Point defects are irregularities produced in the arrangement of the basis at the lattice points of a crystalline solid -- localised disruptions confined to individual lattice sites, as opposed to defects that run along a line or spread through a whole plane of the crystal. There are three major classes of point defect: stoichiometric point defects, in which the compound's chemical formula (its stoichiometry, i.e. the fixed ratio of atoms or of cations to anions) is left unchanged; impurity defects, which arise when foreign atoms different from the host are deliberately or accidentally introduced into the lattice; and non-stoichiometric point defects, in which the ratio of atoms (or cations to anions) genuinely shifts away from the value given by the compound's chemical formula. Each of these three families is examined in its own subsection below, covering, respect …