High-pressure and high-temperature synthesis of rhenium carbide using rhenium and nanoscale amorphous two-dimensional carbon nitride

Abstract

Both Re₂C and Re₂N are ultra incompressible and have a bulk modulus of about 400 GPa. These materials are synthesized under high pressure and high temperature. The synthesis pressures are about 10 GPa or below for Re₂C and 20–30 GPa for Re₂N. If the synthesis pressure of Re₂N was about 10 GPa or below, a large volume high-pressure cell like a multi-anvil apparatus can be used to synthesize Re₂N. To realize this, a proper solid nitrogen source is needed instead of liquid or gas nitrogen. We used a precursor of a mixture of rhenium and home-made nanoscale amorphous two-dimensional carbon nitride as a solid nitrogen source. Consequently, the synthesis reaction produced Re₂C but not Re₂N. We characterized the synthesized Re₂C by various techniques including high-pressure x-ray diffraction (XRD). The bulk modulus B₀ of the synthesized Re₂C under hydrostatic conditions was estimated to be 385.7 ± 18.0 GPa. This value is a little smaller than the previous data. When the pressure medium became non-hydrostatic, the peculiar compression behaviour occurred; the rate of broadening of XRD lines increased and the compression became negligible in the range of a few GPa. The reason for this peculiar behaviour is not known.