High-pressure, high-temperature syntheses in the B-C-N-O system - II. Electron energy-loss spectroscopy (EELS)

Materials with structures related to that of alpha-rhombohedral B (alpha-rh B) were synthesized in the B-C-N-O system at high pressures and temperatures. Electron energy-loss spectroscopy with a transmission electron microscope was used to determine the stoichiometry of these phases. The energy-loss near-edge structure of the core-loss edges provided qualitative information on the bonding and local band structure. Extensive solid solution between B4C and B6O was found in some of the syntheses as well as nanorods with composition near B6C in one experiment. The analysis of the new alpha-rh B-type material, nominally B6N, provided a mean composition of B6N0.92. The B K edge from B6N is similar to that from other icosahedral boron-rich phases, more specifically to B6O, although differences near the conduction-band onset reveal a high level of unoccupied states within the bandgap. (C) 1997 Academic Press.