Frenkel Defect
A point defect in which an ion leaves its lattice site and lodges in a nearby interstitial position.
Unit
Dimensionless
In depth
Since no ion leaves the crystal, both neutrality and density are unchanged, but the dielectric constant rises. Frenkel defects require a large size difference between cation and anion so the small cation can fit into an interstice, and they enhance ionic conductivity.
Examples in the real world
AgBr and AgCl in photographic emulsions; ZnS, where the small Zn²⁺ ion displaces easily.