Question

What is the Frenkel defect? How does it affect the density of the solid?

Answer 1

Hint: Try to remember the definition of Frenkel defect. Frenkel defect is also called a dislocation defect. It is a type of point defect in crystalline solids. It is mostly exhibited in ionic solids where the smaller ion is dislocated.

Complete step by step answer:
 The Frenkel defect forms when an atom or smaller ions leave its place in the lattice, creating a vacancy. It usually occurs in ionic crystals where the size of the anion is quite large as compared to that of the cation. Examples of this defect are $AgBr,ZnS,AgCl$ etc.
Frenkel defect is also known as an interstitial defect as the cation is dislocated from its normal site to the interstitial site. This type of defect is observed in solids when the difference between the ionic radii is large. In this defect, an ion is displaced from its lattice place to an interstitial place. So there is no loss or gain of ions in its lattice structure.
We all know that density is nothing but mass per volume. As there is no change in their mass and volume so there is no effect in the density of the solid due to this defect.

Note:
Don’t get confused between the Frenkel and Schottky defect. The Schottky defect is a vacancy defect which lowers the density of the solid crystal. In this type of defect, the equal number of cation and anion are missing from the interstitial site and it leads to the lowering of density.