<P> In ionic crystals, the defect forms when oppositely charged ions leave their lattice sites, creating vacancies . These vacancies are formed in stoichiometric units, to maintain an overall neutral charge in the ionic solid . The surrounding atoms then move to fill these vacancies, causing new vacancies to form . Normally these defects will lead to a decrease in the density of the crystal . The following are the chemical equations in Kröger--Vink notation for the formation of Schottky defects in TiO and BaTiO . </P> <Dl> <Dd> ∅ ⇌ v + 2 v </Dd> </Dl> <Dd> ∅ ⇌ v + 2 v </Dd> <Dl> <Dd> ∅ ⇌ v + v + 3 v </Dd> </Dl>

Explain with the help of diagrams the important differences in schottky and frenkel defects