Question

Which of the following is a correct statement regarding defects in crystalline solids?
(A) Frekel defect is a dislocation defect
(B) Frenkel defect is found in halides of alkaline metal
(C) Schottkey defects have no effect on the density of crystalline solids
(C) Frenkel defects decrease the density of crystalline solids

Answer 1

Frenkel and Schottky defects are a type of stoichiometric defects found in ionic solids. In the Frenkel defect, the smaller ion gets displaced from its normal site to the interstitial site. Schottky defect is a kind of vacancy defect.

Complete step by step solution:
Although the arrangement of the atoms in the crystals is ordered, they are not perfect. The defects in the crystals are divided into two main categories; line defects and point defects.
- Now, the point defects are classified into three categories in which one category is stoichiometric defects. The stoichiometric defects are the defects which do not alter the stoichiometry of the solid.
- Frenkel and schottky defects are seen in ionic solids.
- Frenkel defect is a dislocation defect. In this effect, the smaller ion which is a cation gets displaced from its normal site to interstitial site. That is the reason why it does not alter the density of the solid. Frenkel defect is seen in the ionic compounds in which there is a large difference in the size of cation and anion. So, compounds like AgCl, AgBr show this defect.
- Schottky defect is a defect in which the site of the ion is found vacant. So, as there is a decrease in the number of atoms per certain volume, this defect decreases the density of the solid.

- Thus, we can say that only the option (A) is a correct statement.

Note: Note that in order to maintain electrical neutrality, the number of positive and negative ions present in the solid having Schottky defect is the same. Schottky defect is seen in the ionic solids which have anions and cations of relatively same size.