Theoretical Investigation of Phase Transitions of Graphite and Cubic 3C Diamond Into Hexagonal 2H Diamond Under High Pressures

Possible techniques for experimentally obtaining hexagonal diamond are studied in the scope of the density functional theory method. It has been found that hexagonal diamond may be created as a result of structural transition at 61–68 GPa uniaxial compression from orthorhombic AB graphite and at 57–66 GPa from hexagonal AA graphite. Also the formation of hexagonal diamond is shown to take place in case of very strong (300–380 GPa) compression of cubic diamond. X‐ray and electron‐microscopic data on nanodiamonds from meteorite craters are analyzed for the presence of hexagonal diamond. The analysis shows that impact‐origin carbon materials do not contain pure cubic and hexagonal diamonds, and the layers of nascent crystals of diamond polytypes are randomly packed.