Experimental and theoretical investigation of Mo2C at high pressure

Molybdenum hemicarbide was investigated by angle-dispersive, x-ray diffraction in a diamond anvil cell at high pressure and by theoretical methods. Mo2C is highly incompressible with a bulk modulus of 307(5) GPa and a first pressure derivative of 6.2(3). Ab initio calculations give values ranging from 291 to 307 GPa for various carbon-ordering schemes. The ordered, orthorhombic form of Mo2C was found to be very slightly lower in energy than the disordered hexagonal phase. The calculated electronic charge distribution clearly indicates a preference for directional molybdenum-carbon bonding.