Question

The type of defect $NaCl$ crystal can exhibit is:

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

Answer 1

The correct option is B Schottky defect

Sodium chloride crystallizes in ccp arrangement. Both sodium and chloride ions are monovalent and of similar sizes. So, they do not exhibit Frenkel defects (cations leaving its lattice sites and occupy interstitial sites).
But on heating the bond is broken and an equal number of sodium and chloride atoms leave the crystal resulting in vacant cationic and anionic sites.
Thus, sodium chloride on heating shows Schottky defect.

Charateristics of schottky defect:
1. This defects observed in solids having small difference in the sizes of cations and anions.
2. They should have high coordination number.
3. Generally shown by highly ionic compounds.
4. Ion–pair vacancies in this defect will decrease density of the solid.
5. The condition of charge neutrality is maintained.
6. Solids like $NaCl,KCl,KBr,AgBr\text{and}CsCl$ shows Schottky defect.
Thus, option (a) is correct.