Question

Why is the Frenkel defect found in $AgCl$ ?

Answer 1

In order to the question, to know why Frenkel defect is found in $AgCl$, first we should know about the frenkel defect and its properties. Then compare the properties with the properties of $AgCl$ .

Complete step-by-step answer: The Frenkel Defect is favoured by a large difference in size between the positive and negative ions. The metal cations are generally smaller than the anions which occupy the vacant lattice site or hole. As we all know in $AgCl$ , $Ag$ contains positively charged ions called cations $(A{g^ + })$ and $Cl$ contains negative charged ions called anions $(C{l^ - })$ . So, cations are small enough in size to fit into interstitial vacant positions. So due to large differences in the size of ions $A{g^ + }$ and $C{l^ - }$ , $A{g^ + }$ occupies voids.

Additional Information: Frenkel defect doesn’t have any effect on the density, mass or volume of the crystal as in the defect migration of ions takes place within the crystal. So, density, mass and volume of the ionic crystal remain the same even after having the frenkel defect.

Note: Sometimes students get confused between the Frenkel Defect and Schottky Defect. So, there are few differences in both of the defects are:
$*$ Schottky Defect reduces the density of the lattice whereas Frenkel Defect doesn’t affect the density of the lattice or atom.
$*$ Due to the Schottky Defect, mass of the lattice is reduced whereas Frenkel Defect doesn’t affect the mass of the lattice.
$*$ Schottky Defect is also known as Valency defect whereas Frenkel Defect also known as dislocation defect.