Question

Cations are present in interstitial sites in ____.
A. Frenkel defect
B. Schottky defect
C. Vacancy defect
D. Metal deficiency defect

Answer 1

Hint:Defects in Stoichiometric Solids: Stoichiometric solids are those in which the number of positive and negative ions are exactly in the ratio indicated by their chemical formulae.
The causes give rise to two types of defects as:
1. Schottky defect
2. Frenkel defect

Complete answer:
Schottky defect: A pair of ‘holes’ or vacancies exists in the crystal lattice due to one cation and one anion missing from the normal lattice sites. The crystal as a whole remains neutral because the number of missing cations and anions remains the same. This sort of defect occurs in highly ionic compounds with a high coordination number and where the ions (both cations and anions) are of similar size.

Frenkel defect: When a ‘hole’ or ‘vacancy’ exists in the crystal lattice because an ion occupies an interstitial lattice site, it gives rise to Frenkel defect. The crystal remains neutral. The defect occurs more frequently in solids which have low coordination number and possess ions (cations and anions) of different sizes. Since cations are generally smaller than anions, it is more common to find the cations occupying the interstitial sites.

Therefore, Option B is the correct answer.

Note:
Metal deficiency defects occur in metals with variable oxidation states, i.e., the transition metals. A cation may be missing from its lattice site but the electrical neutrality is maintained when the adjacent metal ion acquires higher oxidation state