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For example, the twin operation may be reflection across a plane that is not a symmetry plane of the single crystal. [1] [2] On the microscopic level, the twin boundary is characterized by a set of atomic positions in the crystal lattice that are shared between the two orientations.
An example is the Stone Wales defect in nanotubes, which consists of two adjacent 5-membered and two 7-membered atom rings. Schematic illustration of defects in a compound solid, using GaAs as an example. Amorphous solids may contain defects. These are naturally somewhat hard to define, but sometimes their nature can be quite easily understood.
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.
For example, in an ordered AB alloy, if an A atom occupies the site usually occupied by a B atom, a type of crystallographic point defect called an antisite defect is formed. If an entire region of the crystal is translated such that every atom in a region of the plane of atoms sits on its antisite, an antiphase domain is formed.
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.
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 ...
Surface of a nanotwinned copper film with highlighted Σ3 and low angle grain boundaries as imaged by EBSD. Image adapted from Zhao et al. [1] A nanostructured film is a film resulting from engineering of nanoscale features, such as dislocations, grain boundaries, defects, or twinning.
The original use of the term "boundary-work" for these sorts of issues has been attributed to Thomas F. Gieryn, [2] a sociologist, who initially used it to discuss the problem of demarcation, the philosophical difficulty of coming up with a rigorous delineation between what is "science" and what is "non-science". [3] Gieryn defined boundary ...