Which defect alters the density of a crystal lattices?

Options

A. Frenkel defect
B. Metal deficiency defect
C. Schottky defect
D. Metal excess defect

Explanation

To determine which defect alters the density of a crystal lattice, we need to analyze various types of defects in crystal structures. Here’s a step-by-step solution:

### Step 1: Understand Crystal Lattice Defects
Crystal lattices can have defects that can be categorized into two main types: stoichiometric defects and non-stoichiometric defects. Each type can further be classified into subcategories.

### Step 2: Identify Types of Defects
1. **Metal Excess Defect**: This defect occurs when there are extra metal ions in the lattice, often leading to an increase in the number of free electrons. However, this does not change the overall density of the crystal since the mass and volume remain relatively constant.

2. **Metal Deficiency Defect**: This defect occurs when there are fewer metal ions than required by the stoichiometric ratio. Similar to the metal excess defect, this does not significantly alter the density of the crystal lattice.

3. **Schottky Defect**: This defect involves the absence of an equal number of cations and anions from the lattice. Since both types of ions are missing, the overall mass of the crystal decreases while the volume remains the same, leading to a decrease in density.

4. **Frankel Defect**: In this defect, a cation moves to an interstitial site, creating a vacancy in its original position. The overall mass of the crystal remains unchanged, and thus the density does not alter significantly.

### Step 3: Analyze the Effects on Density
- **Metal Excess Defect**: No change in density.
- **Metal Deficiency Defect**: No change in density.
- **Schottky Defect**: Decreases density due to the loss of cations and anions.
- **Frankel Defect**: No change in density.

### Step 4: Conclusion
The defect that alters the density of a crystal lattice is the **Schottky defect**. This defect leads to a decrease in density due to the absence of both cations and anions.

### Final Answer
**The Schottky defect alters the density of a crystal lattice.**

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