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# Schottky defect

A Schottky defect is a type of point defect in a crystal lattice named for Walter H. Schottky. The defect forms when oppositely charged ions leave their lattice sites, creating vacancies. These vacancies are formed in stoichiometric units, to maintain an overall neutral charge in the ionic solid. The vacancies are then free to move about as their own entities. Each vacancy is a separate Schottky defect.Normally these defects will lead to a decrease in the density of the crystal.The following are the chemical equations in Kröger-Vink Notation for the formation of Schottky defects in TiO2 and BaTiO3.

Ø $\Leftrightarrow V_{Ti}'''' + 2V_O^{\bullet \bullet}$

Ø $\Leftrightarrow V_{Ba}'' + V_{Ti}'''' + 3V_O^{\bullet \bullet}$

This can be illustrated schematically with a two-dimensional diagram of a sodium chloride crystal lattice: