Schottky Defect
The Schottky defect arises if some of the atoms or ions are missing from their normal lattice sites. The lattice sites which are abortively are called lattice vacancies or holes. So far as the crystal has to be electrically neutral, an equal number of cations and anions are missing. The ideal AB crystal is shown above. Presence of two holes one due to missing cation and the other due to missing. It is parring excellence a vacancy defect in ionic solids.
The Schottky Defect in a crystal is shown in the image added below.
Conditions for Schottky Defects
This type of defect is usually seen in strong ionic compounds having
- High Coordination number
- Ions of approximately the same size.
For example, NaCl, KCI, KBr, CsCl, and AgBr ionic solids have Schottky defects. It has been ascertained that in NaCl, there are about 106 Schottky pairs per cm³ at room temperature. In 1cm³ there are about 1022 ions and this means that there will be one Schottky defect per 1016 ions in NaCl. Forasmuch as the impendence of a broad number of vacancies in crystals, its density is markedly lowered.
Point Defects
Solids are made up of a lot of small crystals. However, the defect in solids occurs during the crystallization process due to the fast or moderate rate of crystal formation. Defects are described as irregularities in the arrangement of constituent particles in general. The defect could be a point or a line defect based on the irregular arrangement. A deviation point defect occurs in an ideal crystal when there are anomalies in the arrangement around any point or atom in the crystal. Similarly, a line defect occurs when there is a variation in the arrangement of the entire row of lattice points in crystals.
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