Structure of Graphite

Abstract

SINCE the original determination by Bernal1 of the structure of graphite, various alternative structures have been proposed from observations of extra lines and spots on X-ray diffraction photographs. The Bernal structure can be visualized as hexagonal nets of carbon atoms stacked in layers so that half the atoms in one layer are directly above those in the layer below; the other half being above the holes in the first layer. Lipson and Stokes2 were able to show that extra lines on Debye–Scherrer powder photographs of graphite filings could be indexed on the basis of a rhombohedral structure, which can be obtained from the hexagonal structure by shearing a layer a distance |a|/√3 in a direction, where |a| is the lattice parameter of the unit cell in the layer planes. This structure was afterwards verified by X-ray and electron diffraction work on single crystals3. In all cases where it has been found, the rhombohedral modification results from deformation of the original hexagonal structure and can be eliminated by suitable annealing treatments. A second modification of the original hexagonal structure was proposed by Lukesh4 from his observation of satellite spots on c-axis precession photographs of single crystals. This modification results in a large orthorhombic superlattice cell in which the carbon nets are slightly distorted hexagons.