Question

Which of the following statement(s) for crystals having Schottky defect is/are correct?
(A) Schottky defect arises due to absence of cation and anion from the position which it is expected to occupy
(B) Schottky defect are more common in ionic compounds with high coordination numbers
(C) The density of crystals having Schottky defect is larger than that of perfect crystal
(D) The crystal having Schottky defect is electrically neutral as whole

Answer 1

Hint:To solve this, you need to know about the different types of defects found in crystalline solids. Broadly, these defects are classified into two types (a) Point Defects and (b) Line Defects. We mainly focus on Point defects which is further classified into two categories (a) Stoichiometric defect (b) Non- Stoichiometric defect. These defects are further classified into various categories. Schottky defect is a type of stoichiometric defect.

Complete step by step answer:
Point defects arise in the crystalline solid due to a mis arrangement or asymmetry of an atom from the fixed arrangement in the solids.
In stoichiometric defects, the stoichiometry of solids does not change and the ratio of cation and anions remain the same in the crystal. This defect is also known as intrinsic or thermodynamic defects.
This defect is of two types: (a) Vacancy Defects (b) Interstitial Defects.
Vacancy Defects arise due to vacant lattice sites in a crystal which happens generally when the crystal is heated. It leads to a decrease in the density of the solid.
Interstitial defects arise when some atoms or molecules are present at the interstitial sites in the crystal. They increase the density of the solid. They could be foreign or of the same atom.
Schottky Defect is a type of Vacancy defect found in the ionic solids with a high coordination number. This defect arises when an equal number of cations and anions are missing from the crystal creating a ‘Vacancy’ or ‘Hole’.
Since the number of cations and anions missing are equal so, the electrical neutrality of the solid is maintained.

Hence, Option (A), (B), and (D) are correct.

Note:
The occurrence of these defects happens during crystallization (the process of formation of crystals) which occurs at a very fast rate. This happens because during the process the particles don’t get enough time to arrange themselves in a regular pattern.