High-Pressure, High-Temperature Syntheses in the B–C–N–O System

We synthesized severalα-rhombohedral B-rich materials belonging to the B–C–N–O system using a multianvil press. B–C–O materials were prepared by reacting mixtures of B, C, and B2O3in the 5 to 7.5 GPa pressure range and at a temperature of 1700°C. Powder X-ray diffraction and parallel electron energy-loss spectroscopy with a transmission electron microscope showed that the BxCyOzphases obtained are based on theα-rhombohedral B structure. Crystals of composition B6C1.1O0.33to B6C1.28O0.31ranging in size from 1 to 20 μm were grown. Small transparent lustrous red cleavage flakes were obtained for stoichiometries close to B6O. The growth of boron carbide nanorods was also observed in some of the run products. We report the first conclusive bulk synthesis of a new boron nitride, B6N1−x, obtained by reacting B and hexagonal BN at 7.5 GPa and 1700°C. The structure of this compound is derived from that ofα-rhombohedral B (space groupeR3m) and the refined hexagonal cell parameters areah=5.457 Å andch=12.241 Å.