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A twin boundary is a defect that introduces a plane of mirror symmetry in the ordering of a crystal. For example, in cubic close-packed crystals, the stacking sequence of a twin boundary would be ABCABCBACBA. On planes of single crystals, steps between atomically flat terraces can also be regarded as planar defects.
Twin laws are symmetry operations that define the orientation between twin crystal segments. These are as characteristic of the mineral as are its crystal face angles. For example, crystals of staurolite show twinning at angles of almost precisely 90 degrees or 30 degrees. [3] A twin law is not a symmetry operation of the full set of basis ...
Twinning is a phenomenon somewhere between a crystallographic defect and a grain boundary. Like a grain boundary, a twin boundary has different crystal orientations on its two sides. But unlike a grain boundary, the orientations are not random, but related in a specific, mirror-image way. Mosaicity is a spread of crystal plane orientations.
In materials science, a grain boundary is the interface between two grains, or crystallites, in a polycrystalline material. Grain boundaries are two-dimensional defects in the crystal structure , and tend to decrease the electrical and thermal conductivity of the material.
Boundary-work is part of science studies. In boundary-work , boundaries, demarcations, or other divisions between fields of knowledge are created, advocated, attacked, or reinforced. Such delineations often have high stakes for the participants, [ 1 ] and carry the implication that such boundaries are flexible and socially constructed .
The T1 twin type dominates at room temperature and quasi-static strain rates. [35] Twin types present at liquid nitrogen temperature are {112̅2}〈112̅3̅〉(C1 twinning) and {101̅2}〈101̅1〉 (T1 twinning). Secondary twins of another type may form inside the primary twins as the crystal is reoriented with respect to the loading axis. [35]
Depending upon the relative energies of {111} and {110} facets, the shape can range from an icosahedron (on the left of the figure) with small dents at the five-fold axes (due to the twin boundary energy) when {111} is significantly lower in energy, to (going to the right in the figure) a truncated icosahedron or a Icosidodecahedron when the ...
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