Question

Explain the following defects: (i) Interstitial
(ii) F-centred

Hint:

Defects in solids can affect properties like color, conductivity, and density.

Answer 1

(i) Interstitial:

An interstitial defect occurs when an extra atom or ion is inserted into the lattice at a position that is normally unoccupied. This defect leads to a displacement of atoms, resulting in a higher density or strain in the crystal structure.

(ii) F-centred:

An F-centre defect is created when an anion (such as chloride or oxide) is missing from its regular position in the crystal lattice, creating a vacancy. This vacancy is occupied by one or more electrons, which are trapped in the vacancy, giving rise to color changes in the crystal, typically seen in alkali metal halides like sodium chloride (NaCl).