Why ZnS shows dislocation defect ?

Options

A. Small size of both the ions
B. Equal size of both the ions
C. `Zn^+` ions is larger in size
D. `Zn^+` ions is smaller in size

Answer

### Step-by-Step Solution:

1. **Understanding Zinc Sulfide (ZnS)**:
- ZnS is a compound formed from zinc ions (Zn²⁺) and sulfide ions (S²⁻). It is commonly found in nature as the mineral sphalerite.

2. **Defining Dislocation Defects**:
- A dislocation defect in a crystal lattice occurs when there is a misalignment in the arrangement of atoms. This can happen due to the presence of an atom that is not in its normal position, often because of size differences between ions.

3. **Size Difference Between Ions**:
- In ZnS, the zinc ions (Zn²⁺) and sulfide ions (S²⁻) differ significantly in size. The Zn²⁺ ion is smaller compared to the S²⁻ ion. This size disparity leads to the formation of dislocation defects.

4. **Formation of Dislocation Defects**:
- When the larger S²⁻ ions are present in the lattice, the smaller Zn²⁺ ions can occupy interstitial sites (spaces between the regular lattice points). This occupancy of interstitial sites by smaller ions leads to distortions in the crystal structure, resulting in dislocation defects.

5. **Effect on Crystal Density**:
- Despite the presence of dislocation defects, the overall crystal density of ZnS remains relatively unchanged. This is because the defects do not significantly alter the mass or volume of the crystal.

6. **Conclusion**:
- Therefore, ZnS exhibits dislocation defects primarily due to the size difference between the zinc and sulfide ions, which leads to the occupation of interstitial sites by the smaller zinc ions.