Explain the following terms with suitable example:
a. Schottky defect b. Frenkel defect
c. Interstitials d. F-centres

Explanation

a. Schottky defect : It occurs when there is a vacancy of cation and anion sites in the lattice structure.
b. Frenkel defect : It occurs in an ionic crystal when an ion occupies an interstitial position rather than normal site.
c. Interstitials : Atoms of ions which occupy normally vacant interstitals (voids) in a crystal are called interstitials.
d. F-centres: The free electrons trapped in the site of anion vacancies are termed as F-centres.