Schottky Defect
A point defect in which equal numbers of cations and anions are missing from their lattice sites.
Unit
Dimensionless
In depth
Because ions are removed in stoichiometric pairs, electrical neutrality is preserved but the crystal's density falls measurably. Schottky defects are favoured in ionic solids whose cations and anions are of similar size and have high coordination numbers.
Examples in the real world
NaCl, KCl and CsCl show Schottky defects; their measured densities fall slightly below the ideal calculated values.