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Why does AgBr show both Frenkel and Schottky defects ?

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Last updated date: 29th May 2024
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Answer
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Hint :In crystalline solids, crystallographic defects are breaks in regular patterns. Since the positions of atoms or molecules at repeating fixed distances determined by unit cell parameters in crystals with a periodic crystal structure are typically imperfect, they are normal.

Complete Step By Step Answer:
In crystalline solids, crystallographic defects are breaks in regular patterns. Since the positions of atoms or molecules at repeating fixed distances determined by unit cell parameters in crystals with a periodic crystal structure are typically imperfect, they are normal.
Schottky defect
Schottky defect is a form of point defect or imperfection in solids caused by a vacant location in a crystal lattice caused by atoms or ions moving out from the crystal's interior to the surface.
The cation and anion have a very small size difference, which is one of the defect's distinguishing features.
Both the cation and the anion exit the solid crystal.
Atoms leave the crystal permanently as well.
In most cases, two vacancies are created.
The density of the solid decreases significantly.
Frenkel Defect
A Frenkel defect occurs when an atom or cation leaves its original location in the lattice structure to create a void while occupying another interstitial position within the solid crystal.
And when the cations are smaller than the anions does this defect occur. Chemical properties haven't changed either. The Frenkel defect has no effect on the density of the solid, so both its volume and mass are maintained. Substances preserve their electrical neutrality in such situations.
AgBr
Since AgBr's radius ratio is intermediate, it exhibits both Frenkel and Schottky defects. If both anions and cations are absent from the crystal lattice, ions have Schottky defects. Schottky defects are caused by the absence of Ag+ ions and their corresponding Br ions from the crystal lattice in AgBr. However, Ag+ ions are extremely mobile and have a proclivity for moving around within the lattice. As a result, Frenkel defects with Ag+ ions trapped in interstitial spaces are used to complement Schottky defects. Schottky and Frenkel defects occur due to the similar size of Ag+ ions and Br ions, as well as the small size of Ag+ ions and the fact that Ag+ ions are mobile.

Note :
In crystalline solids, crystallographic defects are breaks in regular patterns. Since the positions of atoms or molecules at repeating fixed distances determined by unit cell parameters in crystals with a periodic crystal structure are typically imperfect, they are normal.
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