Question

Frenkel defect does not change the density of the ionic crystal whereas, Schottky defect lowers the density of ionic crystal. Give a reason.

Answer 1

Frenkel defect does not change the density of the ionic crystal. Frenkel defect is observed when cation or anion from ionic solid leaves its regular site and moves to occupy a place between the lattice site called interstitial position. Thus, in this defect, the number of cations and anions remains unchanged. Only their location is changed. Hence, the density of the crystal is not affected.
Schottky defect lowers the density of ionic crystal. In this defect, cations or anions are missing. Due to their vacancies, the mass of crystal deceases but their volume remains same. Hence, there is decrease in the density.