If in an ionic crystal of type A+B− an equal number of cations and anions are missing from their lattice sites so that electrical neutrality, as well as stoichiometry, is maintained, then, this defect is called a Schottky Defect. The presence of holes causes the density of the crystal to decrease. It is a vacancy defect (due to missing ions) and also a stoichiometric defect, as the ratio of the number of cations and anions remains the same. The energy needed to form a Schottky defect is very less but the production of lattice defects of Schottky is an endothermic process. Hence the lattice energy increases. The defect increases the electrical conductivity of the solid due to a migration of the ions into the holes.
