Vacancy defect

In crystallography, a vacancy is a type of point defect in a crystal where an atom is missing from one of the lattice sites.

[2] Crystals inherently possess imperfections, sometimes referred to as crystallographic defects.

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).

[3] 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 the Avogadro constant, and M the molar mass.

In the case of more constrained structures like carbon nanotubes however, vacancies and other crystalline defects can significantly weaken the material.

Electron microscopy of sulfur vacancies in a monolayer of molybdenum disulfide . Right circle points to a divacancy, i.e., sulfur atoms are missing both above and below the Mo layer. Other circles are single vacancies, i.e., sulfur atoms are missing only above or below the Mo layer. Scale bar: 1 nm. [ 1 ]