HIGH-PRESSURE, HIGH-TEMPERATURE SYNTHESES IN THE B-C-N-O SYSTEM - I - PREPARATION AND CHARACTERIZATION

摘要

We synthesized several alpha-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 B2O3 in the 5 to 7.5 GPa pressure range and at a temperature of 1700 degrees C. Powder X-ray diffraction and parallel electron energy-loss spectroscopy with a transmission electron microscope showed that the BxCyOz phases obtained are based on the alpha-rhombohedral B structure. Crystals of composition B6C1.1O0.33 to B6C1.28O0.31 ranging in size from 1 to 20 mu m 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 degrees C. The structure of this compound is derived from that of alpha-rhombohedral B (space groupe R(3) over barm