BN0.5O0.4C0.1: Carbon- and oxygen-substituted hexagonal BN

Abstract

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., BN0.49O0.38C0.11. 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 BN0.5O0.4C0.1, 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.