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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.
where N particle is the number of particles in the unit cell, V particle is the volume of each particle, and V unit cell is the volume occupied by the unit cell. It can be proven mathematically that for one-component structures, the most dense arrangement of atoms has an APF of about 0.74 (see Kepler conjecture), obtained by the close-packed ...
The same packing density can also be achieved by alternate stackings of the same close-packed planes of spheres, including structures that are aperiodic in the stacking direction. The Kepler conjecture states that this is the highest density that can be achieved by any arrangement of spheres, either regular or irregular.
The unit cell is defined as the smallest repeating unit having the full symmetry of the crystal structure. [2] The geometry of the unit cell is defined as a parallelepiped, providing six lattice parameters taken as the lengths of the cell edges (a, b, c) and the angles between them (α, β, γ). The positions of particles inside the unit cell ...
Here there is a choice between separating the spheres into regions of close-packed equal spheres, or combining the multiple sizes of spheres into a compound or interstitial packing. When many sizes of spheres (or a distribution ) are available, the problem quickly becomes intractable, but some studies of binary hard spheres (two sizes) are ...
Projection of unit cell of sigma phase with CrFe structure along c axis Unit cell of μ phase with W 6 Fe 7 structure projected along c-axis. Topologically close pack ( TCP ) phases , also known as Frank-Kasper (FK) phases , are one of the largest groups of intermetallic compounds, known for their complex crystallographic structure and physical ...
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>.
where the sum is over all atoms in the unit cell, ,, are the positional coordinates of the -th atom, and is the scattering factor of the -th atom. [4] The coordinates x j , y j , z j {\displaystyle x_{j},y_{j},z_{j}} have the directions and dimensions of the lattice vectors a , b , c {\displaystyle \mathbf {a} ,\mathbf {b} ,\mathbf {c} } .