Question

Identify the defect developed when an ion of an ionic compound is missing from its regular site and occupies an interstitial position between lattice points.

• A. Schottky defect
• B. Frenkel defect
• C. Substitutional impurity defect
• D. Interstitial impurity defect

Hint:

The key difference between Schottky and Frenkel defects is that Schottky involves the absence of both an anion and cation, whereas Frenkel involves only one ion displaced to an interstitial site.

Answer 1

The Correct Option is B

Step 1: Understand the nature of defects in ionic compounds.
Defects in ionic compounds are categorized into two main types: point defects and line defects. Point defects occur at a specific point in the crystal lattice, and there are several sub-categories of these defects, including Schottky and Frenkel defects.

Step 2: Definition of Schottky Defect.
In the case of a Schottky defect, both an anion and a cation are missing from their respective lattice sites. This results in a decrease in the density of the crystal because both types of ions are absent from the lattice structure.

Step 3: Definition of Frenkel Defect.
In the case of a Frenkel defect, an ion (either an anion or cation) is missing from its regular lattice site and occupies an interstitial position (i.e., a position between lattice points). This defect doesn't significantly change the density of the material as only one ion is displaced to an interstitial site.

Step 4: Other Defects (Substitutional and Interstitial Impurity).
- Substitutional impurity defects occur when an impurity ion replaces a lattice ion.
- Interstitial impurity defects occur when an impurity ion occupies an interstitial position but is not a result of the missing ion in the lattice structure.

Step 5: Final Answer.
In the given problem, the defect where an ion is missing from its regular site and occupies an interstitial position is a Frenkel defect. Therefore, the correct answer is option (2).