Explain Schottky defect and Frenkel defect.

(N/A) $(i)$ Schottky Defect: It is a type of vacancy defect in ionic solids where electrical neutrality is maintained by the absence of an equal number of cations and anions from their lattice sites.
Like a simple vacancy defect,the Schottky defect decreases the density of the substance. The number of such defects is quite significant in ionic solids. For example,in $NaCl$ at room temperature,there are $10^{6}$ Schottky pairs per $cm^{3}$ and about $10^{22}$ ions per $cm^{3}$,meaning there is one Schottky defect per $10^{16}$ ions.
Ionic compounds with high coordination numbers and cations and anions of comparable size exhibit Schottky defects. Examples include $NaCl$,$KCl$,$CsCl$,and $AgBr$.
$(ii)$ Frenkel Defect: This defect is shown by ionic compounds with low coordination numbers and a large difference in the size of the cation and anion. In this defect,the smaller ion (usually the cation) is dislocated from its normal site to an interstitial site. It does not change the density of the crystal. Examples include $ZnS$,$AgCl$,$AgBr$,and $AgI$.