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Question

Which of the following defects in ionic crystals significantly alters the density of the material?

Mr. S M HUSSAIN · Accepted Answer

## CORE INFORMATION
✓ **Answer**: 2 (Schottky defect)
## CONCEPT FRAMEWORK
 **Primary Concept**: Point defects in ionic crystals and their effect on density.
 **Related Topics**: Frenkel defect, Schottky defect, metal excess defects, metal deficiency defects.
 **Prerequisites**: Understanding of ionic crystals, crystal structures, and point defects.
## SOLUTION PATHWAY
**Given Information**:
  The question asks which defect significantly alters the density of an ionic crystal.
  Options are Frenkel defect, Schottky defect, metal excess defect due to anionic vacancies, and metal deficiency defect due to cation vacancies.
**Method & Steps**:
 1. Analyze each defect type and its effect on the number of ions in the crystal lattice.
  Reasoning: Density is directly related to the mass and volume of the crystal.  A change in the number of ions per unit volume will change the density.
 2. Compare the effects of each defect type on the overall number of ions in the crystal lattice.
  Working:
		* **Frenkel defect:** Involves the displacement of an ion from its lattice site to an interstitial site. The total number of ions remains the same; hence, density change is negligible.
		* **Schottky defect:** Involves the creation of cation and anion vacancies in equal numbers. This results in a decrease in the number of ions in the crystal lattice, thus reducing the density.
		* **Metal excess defect due to anionic vacancies:**  Extra metal ions occupy interstitial sites, while anionic vacancies are created. The total number of ions might increase slightly, but the effect on density is usually minor compared to Schottky defects.
		* **Metal deficiency defect due to cation vacancies:** Some cation sites are vacant.  This directly reduces the number of ions in the lattice, reducing the density.
 3. Identify the defect that leads to a significant change in the total number of ions per unit volume.
  Result: Schottky defects cause a noticeable decrease in the density because they create a significant number of vacancies.
  Verification: The decrease in density due to Schottky defects is experimentally observable.
 ## OPTION ANALYSIS
A :x: Frenkel defects do not significantly alter the density because the total number of ions remains the same.
B ✓: Schottky defects significantly reduce the density because they create equal numbers of cation and anion vacancies, leading to a net decrease in ions.
C :x: Metal excess defects due to anionic vacancies only slightly alter density.
D :x: Metal deficiency defects due to cation vacancies reduce density, but usually less than Schottky defects.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing Frenkel and Schottky defects:  Remember that Frenkel involves ion displacement, while Schottky involves vacancy creation.
  2.Ignoring the equal number of vacancies in Schottky defects:  The equal number of cation and anion vacancies is crucial to the density change.
 **Quick Tips**:
  1.Schottky defects always lead to a decrease in density.
  2.Think of the net effect on the number of ions in the crystal lattice.

Mr. S M HUSSAIN · Answer

Frenkel defect

Mr. S M HUSSAIN · Answer

The correct Option is "Schottky defect"

Mr. S M HUSSAIN · Answer

Metal excess defect due to anionic vacancies

Mr. S M HUSSAIN · Answer

Metal deficiency defect due to cation vacancies

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