How does Schottky defect arise ? In which type of ionic compounds does this defect arise ?

Explanation

Schottky Defect. It is a vacancy defect in ionic solids. This defect arises when equal number of cations and anions are missing from the lattice and thus electrical neutrality is maintained. It is shown by those ionicsubstances in which the cations and anions are of almost similar sizes, e.g. CCI, NaCl, KCl and AgBr etc. neutrality is maintained. It is shown by those ionic substances in which the cations and anions are of almost similar sizes, e.g. CCI, NaCl, KCl and AgBr etc.

Due to this defect, density of crystal decreases.