This defect is created in the crystal when the same number of cations and anions are missing from their positions and thus holes (called cation vacancy or anion vacancy) are produced. Since the number of cations and anions that are left in the crystal even after the missing of cations and anions is the same, the crystal remains electrically neutral. The production of two holes, one due to the missing of a cation and the other due to the missing of an anion. Examples of ionic crystals having Schottky defect are NaCl, KCI, KBr, CsCl etc.