Write a short note on Frenkel defect and Schottky defect.

(N/A) Both these defects are observed in ionic solids.
$(i)$ Frenkel Defect: This defect is shown by ionic substances.
The smaller ion (usually cation) is dislocated from its normal site to an interstitial site.
It creates a vacancy defect at its original site and an interstitial defect at its new location. It is also called a dislocation defect.
It does not change the density of the solid. It occurs in ionic solids where there is a large difference in the size of ions. Examples: $ZnS, AgCl, AgBr, AgI$ due to the small size of $Zn^{2+}$ and $Ag^+$ ions.
$(ii)$ Schottky Defect: This is basically a vacancy defect in ionic solids.
To maintain electrical neutrality,the number of missing cations and anions is equal,as shown in the diagram.
Like simple vacancy defects,Schottky defects decrease the density of the substance.