explain schottky defects in detail.
Answers
Schottky defects consist of unoccupied anion and cation sites in a stoichiometric ratio. For a simple ionic crystal of type A−B+, a Schottky defect consists of a single anion vacancy (A) and a single cation vacancy (B), or v•
A + v {\displaystyle \prime } \prime
B following Kröger–Vink notation. For a more general crystal with formula AxBy, a Schottky cluster is formed of x vacancies of A and y vacancies of B, thus the overall stoichiometry and charge neutrality are conserved.
Schottky defects are observed most frequently when there is a small difference in size between the cations and anions that make up a material. They can be 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. When this happens a pair of vacancies is incorporated in the crystal and charge neutrality is maintained. The ion which is missing from the lattice point occupies an interstitial position.
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