Vacancy defect

In crystallography, a vacancy is a type of point defect in a crystal.Crystals inherently possess imperfections, sometimes referred to as crystalline defects. A defect in which an atom is missing from one of the lattice sites is known as a 'vacancy' defect. It is also known as a Schottky defect,although in ionic crystals the concepts are not identical. In crystallography, a vacancy is a type of point defect in a crystal.Crystals inherently possess imperfections, sometimes referred to as crystalline defects. A defect in which an atom is missing from one of the lattice sites is known as a 'vacancy' defect. It is also known as a Schottky defect,although in ionic crystals the concepts are not identical. Vacancies occur naturally in all crystalline materials. At any given temperature, up to the melting point of the material, there is an equilibrium concentration (ratio of vacant lattice sites to those containing atoms). At the melting point of some metals the ratio can be approximately 1:1000. This temperature dependence can be modelled by where Nv is the vacancy concentration, Qv is the energy required for vacancy formation, kB is the Boltzmann constant, T is the absolute temperature, and N is the concentration of atomic sites i.e. where ρ is density, NA Avogadro constant, and A the atomic mass.