Graphite-type hexagonal crystal structure

Graphite exists in two forms alpha and beta. These have identical physical properties, except for their crystal structure. Naturally occurring graphites are reported to contain as much as 30% of the rhombohedral (beta) form, whereas synthetic materials contain only the alpha form. The hexagonal alpha type can be converted to the beta by mechanical treatment, and the beta form reverts to the alpha on heating it above lOOOoC. 

The chemical crystal structure of graphite consists of condensed six-membered rings of carbon atoms forming planar layers. As shown in Fig. 5.3, these layers are stacked in a way that every third layer has an identical position to the first layer, resulting in a stacking sequence A, B A, B A, B etc. " This structure type represents the thermodynamically stable hexagonal crystal stracture. Besides, a... 

The other type of interaction, a ti-ti interaction, is found in crystals of PAHs these are rich in delocalized electrons and mainly consist of sp carbon atoms with peripheral hydrogen atoms attached. Their structures resemble that of graphite in which planar hexagonally disposed layers of carbon atoms are separated by about 4 A. Large PAHs also form molecular complexes with other flat... 

---