Elastic properties, sp³fraction, and Raman scattering in low and high pressure synthesized diamond-like boron rich carbides

Dense BC_xphases with high boron concentration are predicted to be metastable, superhard, and conductors or superconductors depending on boron concentration. However, up to this point, diamond-like boron rich carbides BC_x(dl-BC_x) phases have been thought obtainable only through high pressure and high temperature treatment, necessitating small specimen volume. Here, we use electron energy loss spectroscopy combined with transmission electron microscopy, Raman spectroscopy, surface Brillouin scattering, laser ultrasonics (LU) technique, and analysis of elastic properties to demonstrate that low pressure synthesis (chemical vapor deposition) of BC_xphases may also lead to the creation of diamond-like boron rich carbides. The elastic properties of the dl-BC_xphases depend on the carbon sp²versus sp³content, which decreases with increasing boron concentration, while the boron bonds determine the shape of the Raman spectra of the dl-BC_xafter high pressure-high temperature treatment. Using the estimation of the density value based on the sp³fraction, the shear modulus μ of dl-BC₄, containing 10% carbon atoms with sp³bonds, and dl-B₃C₂, containing 38% carbon atoms with sp³bonds, were found to be μ = 19.3 GPa and μ = 170 GPa, respectively. The presented experimental data also imply that boron atoms lead to a creation of sp³bonds during the deposition processes.