Question

Which of the following is NOT a characteristic of Schottky defect?

• A. After defect stoichiometry, the crystal remains unchanged.
• B. After defect neutrality, the crystal's structure remains unchanged.
• C. After defect density of crystal remains unchanged
• D. It is a vacancy defect.

Hint:

Missing ions mean the crystal gets less dense.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Schottky defect is a vacancy defect in ionic solids. Equal numbers of cations and anions leave the lattice, so the crystal stays electrically neutral. It is common in ionic compounds with similar cation and anion sizes, such as NaCl and CsCl.

Step 2: Effects:
1. Stoichiometry is unchanged, because cations and anions are missing in equal number.
2. The crystal stays neutral.
3. Because ions are missing, the mass per unit volume falls, so the density decreases.

Step 3: Check the options:
(A) is true. (B) is true. (D) is true. (C) says the density remains unchanged, which is false, since vacancies lower the density. So (C) is the statement that is NOT a characteristic.

Final Answer:
Schottky defect lowers density, so option (C) is the odd one. \[ \boxed{C} \]