Which stoichiometric defect does not change the density of the crystal?

Options

A. Frenkel defect
B. Schottky defect
C. Interstitial defect
D. F-centres

Explanation

To solve the question "Which stoichiometric defect does not change the density of the crystal?", we can follow these steps:

### Step 1: Understand Stoichiometric Defects
Stoichiometric defects are imperfections in a crystal lattice that occur without changing the overall composition of the crystal. They can be classified into different types, such as Frenkel defects and Schottky defects.

**Hint:** Familiarize yourself with the types of stoichiometric defects in solids.

### Step 2: Identify the Types of Defects
- **Frenkel Defect:** This defect occurs when an ion (usually a smaller ion) leaves its normal lattice site and occupies an interstitial site. The overall number of ions remains the same, so the density of the crystal does not change.
- **Schottky Defect:** This defect occurs when equal numbers of cations and anions are missing from their lattice sites. This results in a decrease in the density of the crystal.

**Hint:** Compare the characteristics of Frenkel and Schottky defects to determine their effects on density.

### Step 3: Analyze the Impact on Density
In the case of the Frenkel defect, since an ion moves from its lattice position to an interstitial position without any loss of ions, the total mass and volume of the crystal remain unchanged. Therefore, the density of the crystal remains the same.

In contrast, the Schottky defect leads to a reduction in the number of ions in the lattice, which decreases the mass without a corresponding decrease in volume, thus reducing the density.

**Hint:** Consider how the movement of ions affects the overall mass and volume of the crystal.

### Step 4: Conclusion
Based on the analysis, the stoichiometric defect that does not change the density of the crystal is the **Frenkel defect**.

**Final Answer:** The Frenkel defect does not change the density of the crystal.