Question

Why is Frenkel defect not found in pure alkali metal halides?

Answer 1

Schottky defects are basically a vacancy defect in ionic solids that occur due to missing of atoms or ions from the lattice point. In order to maintain electrical neutrality, the number of missing cations and anions are equal. this defect decreases the density of the substance. It is shown by ionic substance in which cation and anion are of all most similar sizes like NaCl, KCl, CsCl.

Frenkel defect is not found in pure alkali metal halides. This is because of the larger size of the cations of the alkali metals, due to the large size the cations cannot fit into the interstitial sites.