Semiconducting Superhard Ruthenium Monocarbide

Abstract

The ruthenium monocarbide (RuC) structure was investigated through a density functional theory based on the 10 structures of known transition-metal compounds. The calculations indicated that zinc blend structured RuC (ZB-RuC) is the most energetically stable at the ground state, and the calculated lattice parameters are more consistent with the experimental values than those recently reported of rock salt structured RuC (RS-RuC). The structural stability of RuC was studied by calculating total energy, elastic constants, and phonon frequencies. Only ZB-RuC showed dynamical stability. It can be concluded that the most likely structure of the synthesized RuC is ZB-RuC rather than RS-RuC. From the calculated band structure and density of states (DOS), it was found that ZB-RuC is a semiconductor while other RuC structures are metallic. The estimated hardness indicates that ZB-RuC is a new superhard material with a Vickers hardness value of 42.8 GPa, compared with B4C. Even though it is a superhard material, the high B/G value (3.95) indicates that ZB-RuC is still a ductile material.