Point defect

A point defect is a localized imperfection involving one or a few atomic sites in a crystal. It may be a missing atom, an extra atom, or an atom of the wrong type.

Crystal lattice: A repeating arrangement of points that describes the periodic structure of a crystal. Point defects are departures from the regular atomic positions represented by a lattice.
Defect formation energy: The energy cost of creating a specified defect in a material. Formation energy helps determine which point defects are thermodynamically favored.
Doping (semiconductors): The intentional addition of impurities to a semiconductor to alter its electrical properties. Substitutional dopants create point defects that supply charge carriers.
Line defect: A one-dimensional crystal imperfection, also called a dislocation. Unlike a point defect, a line defect extends along a line through the crystal.
Vacancy defect: A crystal defect in which an atom or ion is missing from a normally occupied lattice site. A vacancy is the simplest point defect: one lattice site is left unoccupied.
Equilibrium defect concentration: The concentration of defects established by thermodynamic balance at a given temperature. It links defect formation costs to the number of defects present in a crystal.
Color center: A defect in an insulating crystal that absorbs visible light and produces coloration. Certain vacancies trap electrons or holes, giving crystals distinctive optical absorption.
Planar defect: A two-dimensional imperfection in a crystal, such as a grain boundary or stacking fault. Planar defects occupy extended interfaces rather than a few atomic sites.
Interstitial defect: A crystal defect in which an atom occupies a space between regular lattice sites. An interstitial adds an atom without replacing one at a normal lattice site.
Defect migration energy: The energy barrier a defect must overcome to move between positions in a solid. Migration barriers govern whether point defects remain fixed or move through the lattice.

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