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 (alp ha-rh B) were synthesized in the B-C-N-O system at high pressures and temperatures. Electron energy-loss spectroscopy with a transmission el ectron microscope was used to determine the stoichiometry of these pha ses. The energy-loss near-edge structure of the core-loss edges provid ed qualitative information on the bonding and local band structure. Ex tensive solid solution between B4C and B6O was found in some of the sy ntheses as well as nanorods with composition near B6C in one experimen t. The analysis of the new alpha-rh B-type material, nominally B6N, pr ovided a mean composition of B6N0.92. The B K edge from B6N is similar to that from other icosahedral boron-rich phases, more specifically t o B6O, although differences near the conduction-band onset reveal a hi gh level of unoccupied states within the bandgap. (C) 1997 Academic Pr ess.