Explain the terms:
i) schottky defect
ii) Frenkel defect
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Frenkel defect
A Frenkel defect or dislocation defect is a type of defect in crystalline solids where in an atom is displaced from its lattice position to an interstitial site, creating a vacancy at the original site and an interstitial defect at the new location without any changes in chemical properties. This defect appears in ionic solids, and the smaller ion is dislocated. Frenkel defects are often shown by ionic substances with a large difference in the size of ions; e.x. they appear in ZnS, AgCl, AgBr, and AgI due to the small size of the zinc ion with charge +2 and the silver ion with charge +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 surrounding atoms then move to fill these vacancies, causing new vacancies to form. 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.
A Frenkel defect or dislocation defect is a type of defect in crystalline solids where in an atom is displaced from its lattice position to an interstitial site, creating a vacancy at the original site and an interstitial defect at the new location without any changes in chemical properties. This defect appears in ionic solids, and the smaller ion is dislocated. Frenkel defects are often shown by ionic substances with a large difference in the size of ions; e.x. they appear in ZnS, AgCl, AgBr, and AgI due to the small size of the zinc ion with charge +2 and the silver ion with charge +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 surrounding atoms then move to fill these vacancies, causing new vacancies to form. 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.
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Schottky defect:
- Schottky defect is basically a vacancy defect shown by ionic solids.
- In this defect, an equal number of cations and anions are missing to maintain electrical neutrality.
- It decreases the density of a substance.
- Significant number of Schottky defects is present in ionic solids.
- For example, in NaCl, there are approximately 106 Schottky pairs per cm3 at room temperature.
- Ionic substances containing similarsized cations and anions show this type of defect.
- For example: NaCl, KCl, CsCl, AgBr, etc.
Frenkel Defect:
- Ionic solids containing large differences in the sizes of ions show this type of defect.
- When the smaller ion (usually cation) is dislocated from its normal site to an interstitial site, Frenkel defect is created.
- It creates a vacancy defect as well as an interstitial defect.
- Frenkel defect is also known as dislocation defect.
- Ionic solids such as AgCl, AgBr, AgI, and ZnS show this type of defect.
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