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Explain the following terms with suitable examples: (i) Schottky defect (ii) Frenkel defect (iii) Interstitials and (iv) F-centres.

Explain the following terms with suitable examples: (i) Schottky defect (ii) Frenkel defect (iii) Interstitials and (iv) F-centres.

Grade:8

1 Answers

Sunil Kumar FP
askIITians Faculty 183 Points
6 years ago
(1)Schottky defect:-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.
(2)Frenkel defect:-A Frenkel defect, Frenkel pair, or Frenkel disorder is a type of point defect in a crystal lattice. The defect forms when an atom or cation leaves its place in the lattice, creating a vacancy, and becomes an interstitial by lodging in a nearby location
(3)interstitial defect:-interstitials are a variety of crystallographic defects, i.e. atoms which occupy a site in the crystal structure at which there is usually not an atom, or two or more atoms sharing one or more lattice sites such that the number of atoms is larger than the number of lattice sites. They are generally high energy configurations.
(4)F centre-When Potassium chloride is heated in sodium vapour, we see that is acquires a yellow colour. The heating in excess sodium creates new lattice sites for sodium. To maintain the structure, an equal number of chloride sites are also created, but the latter are vacant. The electron of the potassium atom that is ionized in the KCl matrix is trapped by the chloride ion vacancy. This trapped electron can be freed into the crystal by absorbing visible light and hence the colour. A trapped electron at an anion vacancy is an electronic defect and it is known as F centre

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