Crystallographic defect

A disruption of the repeating atomic arrangement in a crystal. Defects include missing atoms, extra atoms, impurities, and distortions that extend through the lattice.

Crystal lattice: A repeating arrangement of points representing the positions and symmetry of a crystal's constituent particles. Defects are departures from this underlying periodic arrangement.
Vacancy: A point defect created when an atom is absent from a lattice site. Thermal motion and processing can leave ordinary lattice sites unoccupied.
Work hardening: The increase in a metal's strength and hardness caused by plastic deformation. Deformation multiplies dislocations, whose interactions impede further motion.
Perfect crystal: An ideal crystal with an indefinitely repeating, defect-free arrangement of atoms or other constituent particles. It is the reference structure from which a crystallographic defect departs.
Unit cell: The smallest repeating structural unit whose translations can reproduce a crystal lattice. Comparing atoms with the repeated unit cell reveals missing or misplaced sites.
Interstitial defect: A defect in which an atom occupies a position between regular lattice sites. Atoms can be inserted into the spaces between the crystal's normal sites.
Doping (semiconductor): The intentional addition of impurities to a semiconductor to control its electrical properties. Substitutional defects supply charge carriers that tune semiconductor behavior.
Grain boundary: An interface separating crystalline regions with different lattice orientations. It is a specific planar defect formed where differently oriented grains meet.
Point defect: A localized imperfection involving one or a few atomic sites in a crystal. Vacancies and substitutions are classified by their limited spatial extent.
Substitutional impurity: A foreign atom that occupies a regular lattice site in a crystal. Impurities disrupt a perfect crystal while replacing its host atoms.

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