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Larger defects in an ordered structure are usually considered dislocation loops. For historical reasons, many point defects, especially in ionic crystals, are called centers: for example a vacancy in many ionic solids is called a luminescence center, a color center, or F-center. These dislocations permit ionic transport through crystals leading ...
Origin of title phenomenon in crystallographic defects. Shown is a two-dimensional slice through a primitive cubic crystal system showing the regular square array of atoms on one face (open circles, o), and with these, places where atoms are missing from a regular site to create vacancies, displaced to an adjacent acceptable space to create a Frenkel pair, or substituted by a smaller or larger ...
Crystals inherently possess imperfections, sometimes referred to as crystallographic defects. Vacancies occur naturally in all crystalline materials. At any given temperature, up to the melting point of the material, there is an equilibrium concentration (ratio of vacant lattice sites to those containing atoms). [ 2 ]
In diamond, only defects of the following symmetries have been observed thus far: tetrahedral (T d), tetragonal (D 2d), trigonal (D 3d, C 3v), rhombic (C 2v), monoclinic (C 2h, C 1h, C 2) and triclinic (C 1 or C S). [2] [4] The defect symmetry allows predicting many optical properties.
F-center in an NaCl crystal. An F-center or color center or Farbe center (from the original German Farbzentrum, where Farbe means color and zentrum means center) is a type of crystallographic defect in which an anionic vacancy in a crystal lattice is occupied by one or more unpaired electrons.
Comparison of fcc and hcp lattices, explaining the formation of stacking faults in close-packed crystals. In crystallography, a stacking fault is a planar defect that can occur in crystalline materials. [1] [2] Crystalline materials form repeating patterns of layers of atoms. Errors can occur in the sequence of these layers and are known as ...
A Schottky defect is an excitation of the site occupations in a crystal lattice leading to point defects named after Walter H. Schottky. In ionic crystals , this defect forms when oppositely charged ions leave their lattice sites and become incorporated for instance at the surface, creating oppositely charged vacancies .
Diffusion creep is caused by the migration of crystalline defects through the lattice of a crystal such that when a crystal is subjected to a greater degree of compression in one direction relative to another, defects migrate to the crystal faces along the direction of compression, causing a net mass transfer that shortens the crystal in the ...