1. General

1.1 Definition

Carbon is known today in three essential forms:

• lediamond, the hardest of all bodies, has a three-dimensional cubic structure (d = 0.351 nm); it is transparent, an electrical insulator and an excellent thermal conductor; it is used mainly in cutting tools and as a die;

• Fulllerenes, a family of spherical molecules comprising 60 to 70 carbon atoms forming a mixed network of hexagons and pentagons like in a soccer; these molecules have just been discovered and their fundamental properties are barely known;

• black varieties, essentially made up of an association of carbon layers; each layer is a two-dimensional hexagonal lattice of carbon atoms, 3 of whose valences...