Crystals possessing CsCl structure change to NaCl structure upon heating. Give a suitable explanation.

Explanation

To explain why crystals possessing a CsCl structure change to a NaCl structure upon heating, we can break down the explanation into clear steps:

### Step-by-Step Solution:

1. **Understanding the Structures**:
- The **CsCl (Cesium Chloride)** structure is characterized by a body-centered cubic arrangement. In this structure, Cl⁻ ions occupy the corners of the cube, while the Cs⁺ ion is located at the body center. This gives a coordination number of 8: each Cs⁺ ion is surrounded by 8 Cl⁻ ions.
- The **NaCl (Sodium Chloride)** structure, on the other hand, has a face-centered cubic arrangement. In this structure, Na⁺ ions occupy the octahedral voids, while Cl⁻ ions form a cubic close-packed (CCP) arrangement. This results in a coordination number of 6: each Na⁺ ion is surrounded by 6 Cl⁻ ions.

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