Question

Explain Schottky and Frenkel defects in solids.

Answer 1

Schottky defect:
Same number of positive and negative ions are missing from their respective positions leaving behind a pair of holes. This defect is more common in ionic compounds with high coordination numbers with approximately equal sizes of cation and anion. The density of the crystal decreases. This defect is observed in $NaCl,CsCl,KCl,KBr,$ etc.

Frenkel defect:
An ion leaves its correct lattice site and occupies an interstitial site. It is common in ionic compounds with low coordination numbers and large differences in the size of cation and anion. This defect is observed in $ZnS,AgCl,AgBr,AgI,$ etc.