An EELS and XAS Study of Cubic Boron Nitride Synthesized under High Pressure - High Temperature Conditions

Cubic Boron Nitride (c-BN) single-crystals have been synthesized under high pressure and high temperature conditions (HP - HT) using hexagonal Boron Nitride (h-BN) precursors. We have performed a study of both phases with electron (EELS) and X-ray (XAS) spectroscopy that are compared. The c-BN ELNES spectra at B-K and N-K edges are found to be consistent with the XANES (XAS) data, although the energy resolution achieved with X-rays is better than that obtained by EELS with a LaB₆ filament. However, XAS is at a disadvantage by comparison with EELS owing to the presence of the N-K edge second order. Attempts were made to dope c-BN with carbon atoms. The examination of the EELS spectra reveals that the incorporation of carbon species in the BN material is always accompanied by the addition of oxygen. Several samples were analyzed both with selected area electron diffraction and energy loss spectroscopy. Most probed crystals containing C (and therefore O) were found to be hexagonal. These results emphasized that the range of existence of the cubic phase is very narrow around the binary composition.