Question

How can you convert CsCl structure into NaCl structure?

Answer 1

1. To convert the CsCl structure into the NaCl structure, the size of the cation must be decreased so that the structure becomes suitable for a lower coordination number.
2. The CsCl structure has a body-centred cubic (BCC) arrangement with a coordination number of 8 : 8, which is stable when the radius ratio `(r_+/r_-)` is greater than 0.732.
3. To achieve the NaCl structure, which is a face-centred cubic (FCC) lattice with a coordination number of 6 : 6, the radius ratio must fall between 0.414 and 0.732.
4. This can be done by replacing the larger Cs⁺ ion with a smaller cation such as Na⁺.
5. The reduced size of the cation leads to a lower radius ratio, which favors the formation of the NaCl structure, where each ion is surrounded by six oppositely charged ions in a more compact FCC arrangement.
6. By reducing the cation size, the structure transitions from CsCl-type (8 : 8 coordination) to NaCl-type (6 : 6 coordination).