Question

Schottky defect is NOT observed in _______.

• A. \( \text{NaCl} \)
• B. \( \text{KCl} \)
• C. \( \text{AgBr} \)
• D. \( \text{NiO} \)

Hint:

To identify crystal defects: - \textbf{Schottky Defect:} Think "similar size" ions (e.g., Na\(^+\)/Cl\(^-\)). This defect decreases the density of the crystal. - \textbf{Frenkel Defect:} Think "large size difference" (e.g., small Ag\(^+\)/large Br\(^-\)). Density remains unchanged.

Answer 1

The Correct Option is C

Step 1: Understand the types of defects. A Schottky defect is a vacancy defect in crystalline solids where a pair of oppositely charged ions are missing from the lattice, maintaining overall electrical neutrality. It is common in highly ionic compounds where the cation and anion are of similar size (e.g., NaCl, KCl).
A Frenkel defect is a defect where an ion (usually the smaller cation) is displaced from its lattice position to an interstitial site. This is common in crystals with a large size difference between the cation and anion.
Step 2: Analyze the options.
- NaCl and KCl are classic examples of compounds showing Schottky defects.
- AgBr is a unique case that shows both Schottky and Frenkel defects. However, it is most commonly cited as an example of a Frenkel defect because the Ag\(^+\) ion is small and can easily move to an interstitial site. Therefore, among the given choices, AgBr is the compound where the Frenkel defect is more prominent and Schottky defect is not the primary defect observed.