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

摘要

Both Re_(2)C and Re_(2)N 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 Re_(2)C and 20–30?GPa for Re_(2)N. If the synthesis pressure of Re_(2)N was about 10?GPa or below, a large volume high-pressure cell like a multi-anvil apparatus can be used to synthesize Re_(2)N. 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 Re_(2)C but not Re_(2)N. We characterized the synthesized Re_(2)C by various techniques including high-pressure x-ray diffraction (XRD). The bulk modulus B_(0) of the synthesized Re_(2)C 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.