BN_0.5O_0.4C_0.1: Carbon- and oxygen-substituted hexagonal BN

Hexagonal boron nitride (hex BN) containing significant amounts of C and O substituting for N (hex BCNO) was synthesized at 75 kbar and 1700°C from mixtures of C, B₂O₃, and amorphous B contained in a hex BN crucible. Hex BCNO is a minor constituent of the product and occurs as small, <30 nm diameter, rounded pseudohexagonal particles adhering to materials with the α-rhombohedral B structure. Electron energy-loss spectroscopy with a transmission electron microscope was used to quantify their elemental ratios. Up to 50% of the N in hex BN is replaced by C and O, e.g., BN_0.49O_0.38C_0.11. The electron energy-loss near-edge fine structure of the core-loss edges was used to elucidate the possible structures of hex BCNO. The core-loss edges of B, C, N, and O exhibit orientation-dependent intensity changes, which indicates that they occupy similar anisotropic bonding sites in graphite-like BCNO layers. For a composition of BN_0.5O_0.4C_0.1, regions with B-N₃, B-N₂O, and B-NO₂ units predominate. In addition, some grains have significant quantities of B-O₃ and B-C₃ units. Boron-boron bonding is either absent or infrequent.