Cubic closest packing ccp

Many pure metals and noble gases adopt the cubic closest packing (ccp) structure of identical spheres, which is based on a face-centered cubic (fee) lattice in space group O- Fm3m. The atomic coordinates and equivalent points of this space group are listed in Table 10.1.1. These data are taken from International Tables for Crystallography, Vol. A. 

Multiplicity Wyckoff position Site symmety Coordinates (o 0,0 0,2 0, 3,0) +  

In three-dimensional closest packing, the spherical atoms are located in position 4(a). There are two types of interstices octahedral and tetrahedral holes which occupy positions 4(b) and 8(c), respectively. The number of tetrahedral holes is twice that of the spheres, while the number of octahedral holes is equal to that of the spheres. The positions of the holes are shown in Fig. 10.1.1. 

The elements with the ccp structure and their unit-cell parameters are listed in Table 10.1.2. 

Multiplicity Wyckoff position Site symmety Coordinates 

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Crystal systems, 75 Cubic closest packed (ccp) system. 120... 

The three cubic lattices simple cubic (SCC) (not used in nature), body-centered cubic (BCC), and face-centered cubic (FCC = cubic closest-packed = CCP). 

The aba arrangement has the hexagonal unit cell shown in Fig. 16.14, and the resulting structure is called the hexagonal closest packed (hep) structure. The abc arrangement has a face-centered cubic unit cell, as shown in Fig. 16.15 on page 779, and the resulting structure is called the cubic closest packed (ccp) structure. Note that in the hep structure the spheres in every other layer occupy the same vertical position (ababab. . . ), while in the ccp structure the spheres in every fourth layer occupy the same vertical position (abcabca. . . ). A characteristic of both structures is that each sphere has 12 equivalent nearest... 

Fig. 2-2. (a) The stacking of close-packed layers in the ABC pattern which, on repetition, gives cubic closest packing, ccp. (b) Another view of the ccp pattern emphasizing its cubic... 

Cubic closest packed (ccp) stmctnre a solid modeled by the closest packing of spheres with an abcabc arrangement of layers the unit cell is face-centered cubic. (10.4)... 

The coordination number of any particular atom in a cubic closest packed (ccp) lattice is 12. Considering an atom in one of the face centres of the diagram in Figure 5.3b, there are four atoms at the comers of the face. Each face of the structure is shared between two such cells, and in the adjacent planes parallel to any shared face there are four atoms. These three sets of four atoms constitute the coordination number of 12. 

Note Face-centered cubic (fee) is equivalent to cubic closest packed (ccp). 

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