Question

What is the defect exhibted by the ionic crystal when the difference in the size of cations and anions is large?

• A. Defectless crystal
• B. Schottky defect
• C. Frenkel defect
• D. Both Schottky and Frenkel defects

Answer 1

The correct option is C Frenkel defect

When an ion is displaced from its regular position to an interstitial position, it creates a vacancy. This defect is called Frenkel defect.

Characteristics of Frenkel defects:
1. It occurs in ionic crystals which having a large difference in size between the positive and negative ions.
2. The coordination number of ionic crystal is usually low (4 or 6).
3. Density of the crystal doesn’t change.
4. $ZnS,AgCl,AgBr\&AgI$ shows Frenkel defects.

Thus,
$AgI$ exhibits Frenkel defect due to large difference in the size of $A{g}^{+}$ and $I^{-}$ ions.