Diffusionless Nucleation of Lonsdaleite and Diamond in Hexagonal Graphite under Static Compression

We have used transmission electron microscopy to study the initial stages of diffusionless formation of lonsdaleite and diamond crystals when pyrolytic graphite is subjected to static compression. We consider the effect of plastic deformation of the matrix phase on development of the transformation. We propose a dislocation model for nucleation of dense phases, making it possible to explain the reason for the formation of a metastable lonsdaleite phase, the nature of its structural disordering, and also the possibility of diffusionless nucleation of diamond directly from hexagonal graphite.