Any deviation from the perfectly ordered arrangement constitutes a defect or imperfection. The compounds in which the number of irregularity are present in the arrangement of atoms or ions are called atomic imperfections or point defects. These may be stochiometric or non - stoichlometric. Stoichiometric defects are further classified into Schottky defects in which number of positive and negative ions are missing in equal ratio and Frenkel defects in which an ion leaves its correct lattice sites and occupies on interstitial site. Schottky defect is more common in ionic compounds with high co-ordination number and where the size of positive and negative ions are almost equal, while in Frenkel defects are common in ionic compounds, which have low co-ordination number and in which there is large difference in size between positive and negative ions.
When an ion leaves ir correct lattice and occupies interstital sites in its crystal lattice, it is called

Options

A. Crystal defect
B. Frenkel defect
C. Schottky defect
D. None

Answer

To answer the question regarding the type of defect that occurs when an ion leaves its correct lattice site and occupies an interstitial site in its crystal lattice, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Crystal Lattice**: A crystal lattice is a three-dimensional arrangement of atoms or ions in a crystalline material. Each atom or ion occupies a specific position in this lattice.

2. **Defining Point Defects**: Point defects are irregularities in the crystal lattice that occur at a single point. These defects can arise from missing atoms or ions (vacancies) or from atoms or ions occupying incorrect positions (interstitials).

3. **Types of Point Defects**: Point defects can be classified into two main categories: stoichiometric defects and non-stoichiometric defects. Stoichiometric defects maintain the overall stoichiometry of the compound, while non-stoichiometric defects do not.

4. **Identifying Stoichiometric Defects**: Stoichiometric defects include:
- **Schottky Defect**: This occurs when equal numbers of cations and anions are missing from the lattice, creating vacancies.
- **Frenkel Defect**: This occurs when an ion leaves its lattice position and occupies an interstitial site, creating a vacancy at its original position.

5. **Frenkel Defect Explanation**: In the case of the Frenkel defect, an ion (typically a cation) moves from its regular lattice site to an interstitial site. This movement creates a vacancy where the ion was originally located.

6. **Conclusion**: Therefore, when an ion leaves its correct lattice site and occupies an interstitial site in its crystal lattice, it is specifically referred to as a **Frenkel Defect**.

### Final Answer:
The defect that occurs when an ion leaves its correct lattice site and occupies an interstitial site in its crystal lattice is called a **Frenkel Defect**.

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