Which of the following is a non-stoichiometric defect ?

Options

A. Frenkel defect
B. Schottky defect
C. metal deficiency defect
D. interstitial defect

Explanation

To determine which of the following is a non-stoichiometric defect, we need to understand the types of defects in solids, particularly in ionic crystals. Non-stoichiometric defects are those that alter the stoichiometric ratio of the ions in the crystal lattice.

### Step-by-Step Solution:

1. **Understanding Defects in Crystals**:
- Crystals can have defects that can be classified into two main categories: stoichiometric and non-stoichiometric defects.
- Stoichiometric defects maintain the overall ratio of cations to anions, while non-stoichiometric defects do not.

2. **Types of Defects**:
- **Schottky Defect**: This defect occurs when an equal number of cations and anions are missing from the lattice. The overall stoichiometric ratio remains unchanged.
- **Frenkel Defect**: This defect occurs when an ion (cation or anion) is displaced from its normal position to an interstitial site, but the overall stoichiometry remains the same.
- **Metal Deficiency Defect**: This defect occurs when there is a deficiency of metal cations in the lattice, leading to a change in the stoichiometric ratio of the ions.
- **Interstitial Defect**: This defect occurs when extra ions occupy interstitial sites, but it does not change the overall stoichiometric ratio.

3. **Identifying Non-Stoichiometric Defects**:
- Among the defects mentioned, the **Metal Deficiency Defect** is a non-stoichiometric defect because it changes the ratio of cations to anions in the crystal lattice.

4. **Conclusion**:
- Therefore, the non-stoichiometric defect among the options provided is the **Metal Deficiency Defect**.

### Final Answer:
The non-stoichiometric defect is the **Metal Deficiency Defect**.

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