Question

Define Frenkel defect in solid crystal.

Answer 1

Hint: We know that the defects arise when an atom or ion goes missing or dislocates from the crystal lattice or any atom gets added to the crystal lattice. In stoichiometric defects, the ratio of cations and anions does not change. In non-stoichiometric defects, the ratio of cations and anions changes.

Complete Step by step answer:Frenkel defect was discovered by Yakov Frenkel. It is a type of point defect and is also known as dislocation defect. Frenkel defect is generally exhibited by ionic solids. Smaller ions are dislocated when Frenkel defect occurs.
The defect formed when the smaller atom or ion (usually cation) leaves its original place in the crystal lattice and creates a vacancy in the crystal lattice is known as Frenkel defect. The cation occupies another interstitial position in the crystal lattice.
Some examples of Frenkel defects are ${\text{AgBr, ZnS, AgCl}}$, etc.
Frenkel defect is known as interstitial defect as cation dislocates from its normal site to the interstitial site. Frenkel defect occurs when the difference between the ionic radii of the cation and anion is large.
No loss or gain of ions occurs in the Frenkel defect and thus, the density does not change when the Frenkel defect occurs. Also, mass and volume of the crystal do not change when a Frenkel defect occurs.

Note: Another type of defect that occurs in a solid crystal is Schottky defect. Schottky defect occurs in solids in which the difference between the ionic radii of the cation and anion is not very large. ${\text{AgBr}}$ shows both Frenkel as well as Schottky defect.