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Facecentered cubic (fcc) crystals are common among metals at low temperatures because the atoms pack well. Steels are bodycentered cubic at low temperatures and facecentered cubic at high temperatures. For FCC and HCP systems, the coordination numbers are 12, while for BCC it’s 8. Assuming a hard sphere model, atomic packing factor is defined as the ratio of atomic sphere volume to unit cell volume, which is 74% for both FCC and HCP and 68% for BCC. In general, ~90% elemental metals crystallize into three crystal structures which are BCC, FCC, and HCP.
Table 2872a. Some normalized surface energies of lowindex surfaces of fcc.
Solid

(100)

(110)

(111) 
(311) 
(531) 
(210) 







Table 2872b lists the characteristics of the three cubic Bravais lattices.
Table 2872b. The only three cubic Bravais lattices.
Lattice 
Number of
lattice points
per unit cell 
Number of
atoms
per unit cell 
Nearest distance
between lattice points 
Maximum packing 
Maximum packing condition 
Density (or fraction of packing, V_{atom}/V_{cell}) 

1 
1 

When the adjacent atoms touch each other along the edge
of the cube 
52.4% 

2 
2 

When the adjacent atoms touch each other along
the body diagonal of the cubic cell 
68.0% 
FCC 
4 
4 

When the adjacent atoms touch each other along
the face diagonal of the cubic cell 
74.0% 

4 
8 


34 % 
For FCC and BCC structures, the lattice constants are given by, (For FCC, you can download the excel file for your own calculations)
 [2872]
Table 2872c. Other characteristics of FCC structures.
Contents 
Page 
Close packed planes and directions 
page3029 
Atomic packing factor 
page3030 
Number of lattice points (atoms) per unit cell 
page3032 
Lattice point (or called Motif or basis) 
page3076 
Coordination number of atoms 
page3031 
Space groups 
Fm3m (225), F43m (216), Fd3m (227), Pm3m (221) 
dspacing ratios of allowed Bragg reflections 
1, √3, √4, √8, √11, √12, √16, √19, √20, √24, √27, ... 
Tables of Burgers vectors of dislocations and g·b 
page1995 
Dominating slip planes, slip directions and stable Burgers vector for common crystal structures 
page3557 
Digital Micrograph script to compute reflection angle 
Script link 
Figure 2872a. Atomic structure of FCC.
