Question

Which of the following defects in the crystals may lower the density?

• A. Frenkel defect
• B. Interstitial defect
• C. Schottky defect
• D. Vacancy defect

Answer 1

Answer: (C), (D)

Vacancy defect

Interstitial defect :-
This is a crystallographic defects, where additional atoms are present in a normally unoccupied interstial sites in the crystal structure. These defects are not observed in ionic solid. Rather than showing simple vacancy or interstitial defects, such ionic solids show Frenkel and Schottky defects.
Density increases as number of atoms per unit volume increases.

Vacancy defect :-
It is a type of point defect in a crystal when some of the lattice sites in the crystal are vacant. Since the number of particles per unit area is reduced, the density of the solid decreases.

Schottky defect :-
In Schottky defect, pair of one cation and one anion of equal valence is missing from an ionic crystal resulting in formation of pair of vacant sites. These ion–pair vacancies decrease density of the solid.

Frenkel defect :-
In Frenkel defect an ion is displaced from its regular position to
an interstitial position. It does not left the crystal so density of a solid does not change.

Hence, options (b) and (c) are the correct answers.