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Article: Crystallographic defect

Crystallographic defect

Point Defects

  • Point defects occur at or around a single lattice point
  • They are not extended in space
  • Point defects typically involve a few extra or missing atoms
  • Larger defects in an ordered structure are considered dislocation loops
  • Point defects in ionic crystals are often called centers, such as vacancies being called luminescence centers or F-centers

Vacancy Defects

  • Vacancy defects are lattice sites that are vacant in a perfect crystal
  • Neighboring atoms may move to occupy the vacant site, causing the vacancy to move in the opposite direction
  • The stability of the crystal structure prevents neighboring atoms from collapsing around the vacancy
  • In some materials, neighboring atoms may move away from a vacancy due to attraction from surrounding atoms
  • A vacancy (or pair of vacancies in an ionic solid) is sometimes called a Schottky defect

Interstitial Defects

  • Interstitial defects are atoms that occupy a site in the crystal structure where there is usually not an atom
  • They are generally high energy configurations
  • Small atoms, like hydrogen in palladium, can occupy interstices without high energy
  • A nearby pair of a vacancy and an interstitial is often called a Frenkel defect or Frenkel pair
  • Interstitial defects can affect the transport of atoms through crystals

Substitutional Defects

  • Substitutional defects occur when an impurity atom is incorporated at a regular atomic site in the crystal structure
  • The substituting atom may have a different oxidation state than the atom it is replacing (aliovalent substitution)
  • Substitutional defects can shift the equilibrium position of the substituting atom away from the lattice site
  • Off-center ions are substitutional defects where the substituting ion is substantially smaller than the ion it is replacing
  • Isovalent substitution occurs when the substituting ion has the same oxidation state as the ion it is replacing

Other Types of Defects

  • Antisite defects occur when atoms of different types exchange positions in an ordered alloy or compound
  • Topological defects are regions in a crystal where the normal chemical bonding environment is topologically different from the surroundings
  • Amorphous solids can contain defects, such as dangling bonds in ideally bonded amorphous silica
  • Complexes can form between different kinds of point defects, such as vacancies binding with impurities
  • Line defects, such as dislocations and disclinations, also contribute to crystallographic defects

Crystallographic defect Data Sources

Reference URL
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