Info

conductivity along the c-axis (see Fig. 2.2) [2.3], In contrast to the semimetallic anisotropic graphite phase, diamond is an isotropic, cubic, wide-gap (5.5 eV) insulator [2.5]. In terms of mechanical properties, graphite is the stiffest material in nature (has the highest in-plane elastic modulus), while diamond is the hardest (least deformable) material. Of

Fig. 2.2. The crystal structure of hexagonal single crystal graphite with D\h (P6}/mmc) space group symmetry. The planes of carbon (graphene layers) are stacked in an .. .ABAB... sequence [2.4], The A and B carbon sites are denoted by open circles and the A' and B' sites by black circles. The in-plane lattice constant is denoted by «„, and the vectors of the unit cell in the directions a,, a2 and c are indicated. The nearest-neighbor carbon distance ac_c in graphite is 1.421 À.

Fig. 2.2. The crystal structure of hexagonal single crystal graphite with D\h (P6}/mmc) space group symmetry. The planes of carbon (graphene layers) are stacked in an .. .ABAB... sequence [2.4], The A and B carbon sites are denoted by open circles and the A' and B' sites by black circles. The in-plane lattice constant is denoted by «„, and the vectors of the unit cell in the directions a,, a2 and c are indicated. The nearest-neighbor carbon distance ac_c in graphite is 1.421 À.

all materials, diamond along with graphite (in-plane) exhibits the highest thermal conductivity and the highest melting point [2.6,7]. Diamond also has the highest atomic density of any solid (see Table 2.1). Graphite and diamond are two main allotropic forms of bulk carbon. Fullerenes and carbon nanotubes, as discussed in this volume, constitute other allotropic

Table 2.1

Properties of graphite and diamond

Table 2.1

Properties of graphite and diamond

Property

Graphite"

Diamond

Lattice structure

Hexagonal

Cubic

Space group

P^/mmc (D\h)

Fd3m (Ol)

Lattice constant6 (Ä)

Was this article helpful?

0 0

Post a comment