Frenkel defect

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A Frenkel defect, also called a Frenkel pair or Frenkel disorder, is a compound crystallographic defect in which an interstitial lies near the vacancy. A Frenkel defect forms when an atom or ion leaves its place in the lattice (leaving a vacancy), and lodges nearby in the crystal (becoming an interstitial). The phenomenon is named after the Russian physicist Yakov Frenkel.

For example, consider a lattice formed by X and M ions. Suppose an M ion leaves the M sublattice, leaving the X sublattice unchanged. The number of interstitials formed will equal the number of vacancies formed.

This can be illustrated with the example of the sodium chloride crystal structure. The diagrams below are schematic two-dimensional representations. This defect was discoverd by a russian scientist Frenkel in 1926.It arises when an ion is missing from its normal position and occupies an interstitial site between the lattice points.