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A Schottky defect is a type of point defect in a crystal lattice named after Walter H. Schottky. In non-ionic crystals it means a lattice vacancy defect. In ionic crystals, 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 followings are the chemical equations in Kröger-Vink Notation for the formation of Schottky defects in TiO2 and BaTiO3. Ø Ø This can be illustrated schematically with a two-dimensional diagram of a sodium chloride crystal lattice: ==Definition== If in an ionic crystal of type A+B− an equal number of cations and anions are missing from their lattice sites so that electrical neutrality as well as stoichiometry is maintained, then, this defect is called a Schottky Defect. It is a vacancy defect (due to missing ions) and also a stoichiometric defect, as the ratio of the number of cations and anions remains the same. It occurs only when there is small difference in size between cations and anions. This is produced as the result of the thermal incorporation of unoccupied lattice sites from the exterior of the crystal. The lattice undergoes thermal vibration and thermal expansion when the temperature is raised above 0K. When it happens the pair of vacancies are incorporated in the crystal. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Schottky defect」の詳細全文を読む スポンサード リンク
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