Question

Explain the following terms:
i. Substitutional impurity defect
ii. Interstitial impurity defect

Hint:

Substitutional defects involve atom replacement, while interstitial defects involve atoms in lattice voids.

Answer 1

i. Substitutional Impurity Defect: Occurs when an atom in a crystal lattice is replaced by a different type of atom. For example, in a silicon crystal, a phosphorus atom may substitute a silicon atom, altering electrical properties (used in doping semiconductors).
ii. Interstitial Impurity Defect: Occurs when a foreign atom occupies an interstitial (empty) site in the lattice, not replacing any host atom. For example, carbon atoms in iron form interstitial defects, increasing hardness in steel.