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[1] [2] Highest density is known only for 1, 2, 3, 8, and 24 dimensions. [3] Many crystal structures are based on a close-packing of a single kind of atom, or a close-packing of large ions with smaller ions filling the spaces between them. The cubic and hexagonal arrangements are very close to one another in energy, and it may be difficult to ...
Unit cell of an fcc material. Lattice configuration of the close packed slip plane in an fcc material. The arrow represents the Burgers vector in this dislocation glide system. Slip in face centered cubic (fcc) crystals occurs along the close packed plane. Specifically, the slip plane is of type , and the direction is of type < 1 10>.
Line dislocations tend to occur on the closest packed plane in the closest packed direction. For an FCC crystal, the closest packed plane is the (111) plane, which becomes the glide plane, and the closest packed direction is the [110] direction. Therefore, a perfect line dislocation in FCC has the burgers vector ½<110>, which is a ...
This type of structural arrangement is known as cubic close packing (ccp). The unit cell of a ccp arrangement of atoms is the face-centered cubic (fcc) unit cell. This is not immediately obvious as the closely packed layers are parallel to the {111} planes of the fcc unit cell. There are four different orientations of the close-packed layers.
An edge dislocation is a defect where an extra half-plane of atoms is introduced midway through the crystal, distorting nearby planes of atoms. When enough force is applied from one side of the crystal structure, this extra plane passes through planes of atoms breaking and joining bonds with them until it reaches the grain boundary.
Note: the term fcc is often used in synonym for the cubic close-packed or ccp structure occurring in metals. However, fcc stands for a face-centered cubic Bravais lattice, which is not necessarily close-packed when a motif is set onto the lattice points. E.g. the diamond and the zincblende lattices are fcc but not close-packed. Each is ...
Close packed surfaces such as the fcc (111) tend to have higher diffusion rates than the correspondingly more "open" faces of the same material such as fcc (100). [10] [11] Directional anisotropy refers to a difference in diffusion mechanism or rate in a particular direction on a given crystallographic plane.
A close packed unit cell, both face-centered cubic and hexagonal close packed, can form two different shaped holes. Looking at the three green spheres in the hexagonal packing illustration at the top of the page, they form a triangle-shaped hole. If an atom is arranged on top of this triangular hole it forms a tetrahedral interstitial hole.