What is Frenkel defect?

What is Frenkel defect?
Chemistry Question Answer
Chemistry Question Answer

What is Frenkel defect?

Frenkel defect is a class of point defects in crystalline materials. It occurs when an atom or ion is displaced from its regular position in the crystal lattice to a nearby interstitial position, creating a vacancy at the original site. This can occur due to the absorption of energy, such as from irradiation or thermal energy, or from the presence of impurities in the crystal.

What is Frenkel defect?

Frenkel defect does not change the density of the solid. This defect is common when the difference in ionic radii of cations and anions is large. The main conditions for Frenkel defects are:
(i) Coordination number should be low
(ii) Size of the anion should be bigger than the cation.
Frenkel defects are mostly exhibited in ionic solids where the smaller ion (usually the cation) is dislocated. Some examples are AgBr, ZnS, AgCl, and AgI.
The defect is not found in alkali metal halides because cations and anions have almost equal sizes and cations cannot be accommodated in interstitial sites.

Frenkel defects can affect the properties of the material, such as its conductivity and mechanical strength. In some cases, Frenkel defects can also lead to the formation of color centers, which can absorb light and give the material a characteristic color.


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