Noun
Frenkel defect (plural Frenkel defects)
(crystallography) A type of point defect in crystalline solids, occurring when an atom or smaller ion (usually cation) leaves its place in the lattice, creating a vacancy, and becomes an interstitial by lodging in a nearby location.
Schematic illustration of some simple point defect types in a monatomic solid *A nearby pair of a vacancy and an interstitial is often called a Frenkel defect or Frenkel pair. Source: Internet