vacancyinterstitial

Vacancyinterstitial, also known as a vacancy–interstitial defect, is a type of point defect in crystalline solids characterized by the presence of a vacancy at a lattice site and an atom occupying an interstitial site. The defect forms when an atom is displaced from its regular lattice position and becomes accommodated in a neighboring interstitial site, leaving behind a vacant lattice site.

These defects preserve the overall chemical composition and, in ionic crystals, charge neutrality. They are favored in crystals with open structures or with small, mobile ions, and are often observed in ionic compounds such as AgCl, AgBr, ZnS, and CuCl. In metals, vacancy–interstitial pairs can form under irradiation or at high temperatures but are generally less prevalent than diffusion via vacancies or self-interstitials; diffusion can occur through the vacancy mechanism or, for very small interstitials, via interstitial diffusion.

The presence of vacancyinterstitial defects influences diffusion rates, electrical conductivity, and optical properties. Their concentration follows an Arrhenius-type temperature dependence, governed by the formation energy of the vacancy–interstitial pair and the migration energy required for the defects to move through the lattice.

Relation to other defects: The vacancyinterstitial pair is related to other point defects, notably Frenkel defects (a specific case in which a cation or anion leaves its lattice site to an interstitial position) and Schottky defects (paired vacancies of different ion species in ionic crystals).