Question

Which of the following show both Frenkel and Schottky defect?

• A. ZnS
• B. AgBr
• C. NaCl
• D. AgCl

Hint:

Remember: AgBr is a special compound that shows both Frenkel and Schottky defects due to the size and mobility of the Ag$^+$ ion.

Answer 1

The Correct Option is B

Frenkel Defect: This defect occurs when a smaller ion (usually a cation) leaves its lattice site and occupies an interstitial site. This does not change the overall stoichiometry or electrical neutrality. It is common in compounds where the cation is small in size and the anion is comparatively larger.
Schottky Defect: This defect occurs when equal numbers of cations and anions are missing from the lattice, thereby maintaining electrical neutrality. It is more common in ionic compounds with high coordination numbers and where the size of cation and anion is similar.
AgBr (Silver Bromide) is unique because:
- It shows Schottky defect due to missing equal numbers of Ag$^+$ and Br$^-$ ions.
- It also exhibits Frenkel defect because Ag$^+$ ions are small and can occupy interstitial sites.
Hence, AgBr shows both Frenkel and Schottky defects.
Other options:
- ZnS shows only Frenkel defect.
- NaCl shows only Schottky defect.
- AgCl usually shows only Frenkel defect.