handbook of carbon, graphite, diamond and fullerenes

46 Carbon, Graphite, Diamond, and Fullerenes
Other characteristics of the graphite crystal are the following;
• The crystallographic description is given by the space group
D 4 6H-P63/mmc.
• The crystal lattice parameters, i.e., the relative position of its
carbon atoms (along the orthohexagonal axes) are: a,, = 0.245
nm and c0 = 0.6708 nm.
• The common crystal faces are {0002}, {1010}, {1011} and
{1012}.
• The crystal cleavage is {0002} with no fracture.
• The crystal is black and gives a black streak.
• Hexagonal graphite is the thermodynamically stable form of
graphite and is found in all synthetic materials.
Rhombohedral Graphite. The other graphite structure is rhombohedral
with the stacking order -ABCABCABC-. The carbon atoms in every
third layer are superimposed. The crystallographic description is given by
the space group D 5 ^ -R3m. The crystal lattice parameters are: e^ = 0.2256
nm and c0 = 1.006 nm. A view of the stacking sequence perpendicular to
the basal plane is given in Fig. 3.3.
Plane A
Plane B
Plane C
Figure 3.3. Schematic of rhombohedral graphite crystal. View is perpendicular to
basal plane.