Question

What are the consequences of Frenkel defects in crystals?

Answer 1

1. In a Frenkel defect, a cation shifts from its regular lattice site to an interstitial site, resulting in no change in density.
2. Since no ions are removed from the crystal, the mass and volume remain unchanged, so the density stays the same.
3. Maintaining stoichiometry and electrical neutrality, the total number of positive and negative ions remains the same, preserving both the chemical composition and electrical neutrality of the crystal.
4. Ionic conductivity increases because the presence of vacant and interstitial sites allows ions to move more freely, especially at elevated temperatures. 
5. Lattice distortion is the displacement of ions into interstitial positions because of local distortion in the crystal structure, which may slightly affect its mechanical properties.
6. It is commonly observed in crystals with a large difference in the size of cations and anions, like AgCl, ZnS, and AgBr.