The statements which are the about stoichiometric defects

Options

A. the density may be less than pure crystal
B. the density must be less than pure crystal
C. the electrical and thermal conductivity may be more than pure crystal
D. the electrical and thermal conductivity must be more than pure crystal

Answer

To solve the question regarding the statements about stoichiometric defects, we will analyze the properties of two types of stoichiometric defects: Schottky defects and Frankel defects.

### Step-by-Step Solution:

1. **Understanding Stoichiometric Defects**:
- Stoichiometric defects are imperfections in a crystal lattice that maintain the overall stoichiometry of the compound. The two main types are:
- **Schottky Defect**: This defect occurs when an equal number of cations and anions are missing from the lattice, creating vacancies.
- **Frankel Defect**: This defect occurs when a cation leaves its lattice site and occupies an interstitial site, creating a vacancy in the lattice.

2. **Effect on Density**:
- In **Schottky defects**, the removal of ions from the lattice leads to a decrease in density because there are fewer ions in the lattice structure.
- In **Frankel defects**, since only one ion migrates to an interstitial site and no ions are removed from the lattice, the density remains constant.

3. **Evaluating the Statements**:
- **Statement 1**: "Density may be less than the pure crystal."
- This statement is **correct** for Schottky defects, as the density decreases due to missing ions.
- **Statement 2**: "Density must be less than the pure crystal."
- This statement is **incorrect** because in Frankel defects, the density remains constant.
- **Statement 3**: "Electrical and thermal conductivity may be more than pure crystals."
- This statement is **correct** for Schottky defects, as the increase in vacancies enhances conductivity.
- **Statement 4**: "Electrical and thermal conductivity must be more than pure crystals."
- This statement is **incorrect** for Frankel defects, as the conductivity does not increase significantly.

4. **Conclusion**:
- The correct statements regarding stoichiometric defects are:
- Statement 1 is correct: "Density may be less than the pure crystal."
- Statement 3 is correct: "Electrical and thermal conductivity may be more than pure crystals."

### Final Answer:
The correct statements about stoichiometric defects are:
1. Density may be less than the pure crystal.
3. Electrical and thermal conductivity may be more than pure crystals.