SIMULTANEOUS CRYSTALLIZATION OF DIAMOND AND CUBIC BORON-NITRIDE FROM THE GRAPHITE RELATIVE BC2N UNDER HIGH-PRESSURE HIGH-TEMPERATURE CONDITIONS

Graphitic BC2N has been compressed with Co metal at a pressure of 5.5 GPa and temperatures of 1400-1600-degrees-C. The principal resulting products were crystals (average dimension 3 mum) with cubiclike facets. The powder X-ray diffraction pattern revealed two kinds of cubic phase, in approximately equal amounts, which were identified as diamond and cBN on the basis of their lattice parameters. Microelemental analyses on individual crystal fragments by K-edge electron energy-loss spectroscopy confirmed this disproportionating crystallization scheme: half of the grains were composed of carbon-only signals of which gave fine-structure characteristic of sp3 bonding and the other half gave spectra characteristic of sp3 boron and nitrogen. The crystallization of cBN as well as diamond in the catalytic solvent of pure Co metal is observed here for the first time and is of relevance to the mechanism of the accepted catalytic action of cobalt on the hexagonal/cubic transformation.