Structural features of heavily boron-doped graphite and diamond microcrystals synthesized at high pressures

Abstract

Heavily boron-doped graphite was synthesized from a mixture of adamantane and boron using a high-pressure technique. Ab initio calculations of a carbon cluster of 64 atoms located in two layers of graphene with the inclusion of one boron atom were made. Substitution of boron for carbon in the graphene layer correlates with the experimental data if we consider the change in the cell parameters. The easy transformation of the boron-doped graphite lattice into a diamond one at pressure of about 7.5 GPa may be due to the presence of a small number of boron atoms between graphene layers. Heavily boron-doped diamond crystals in the shape of a five-pointed star were found. The mechanism of their growth includes cyclic twinning and is obviously associated with the presence of a fluid phase in the synthesis medium and facilitated twinning of a diamond lattice containing boron.