Schottky defect

Schottky defects are created when equal number of cations and anions are missing from some ionic compound.Thus stoichiometry of the solid remains same.Schottky defect decreses density of crystal .A Schottky defect is a type of point defect in a crystal lattice named after 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. 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:

The defect-free NaCl structure

Schottky defects within the NaCl structure

See also

• Frenkel defect
• Wigner effect
• Crystallographic defects

References

Kittel, Charles, Introduction to Solid State Physics - 8th ed. Wiley, 2005. ISBN 0-471-41526-X.