Frenkel defect

[1] The defect forms when an atom or smaller ion (usually cation) leaves its place in the structure, creating a vacancy and becomes an interstitial by lodging in a nearby location.

[2] In elemental systems, they are primarily generated during particle irradiation, as their formation enthalpy is typically much higher than for other point defects, such as vacancies, and thus their equilibrium concentration according to the Boltzmann distribution is below the detection limit.

In ionic compounds, the vacancy and interstitial defect involved are oppositely charged and one might expect them to be located close to each other due to electrostatic attraction.

[4] Even though Frenkel defects involve only the migration of the ions within the crystal, the total volume and thus the density is not necessarily changed: in particular for close-packed systems, the structural expansion due to the strains induced by the interstitial atom typically dominates over the structural contraction due to the vacancy, leading to a decrease of density.

[citation needed] Frenkel defects are exhibited in ionic solids with a large size difference between the anion and cation (with the cation usually smaller due to an increased effective nuclear charge) Some examples of solids which exhibit Frenkel defects: These are due to the comparatively smaller size of