Ultra-incompressible superconducting phase of OsC predicted by phonon calculations

The earlier proposed WC-type and NiAs-type structures of the synthesized potential superhard material OsC were found to be dynamically unstable at ambient pressure by ab initio phonon calculations. An energetically more favorable phase with the orthorhombic Pmn21 structure consisted of pyramids was then predicted by employing frozen-phonon technique. The Pmn21 structure is stable up to about 80 GPa and then transforms to the WC-type structure. Results show that OsC with the Pmn21 structure is an ultra-incompressible material originated from the three-dimensional network of the covalent Os-C bond. Electronic and electron-phonon coupling calculations suggest that the Pmn21 OsC is metallic and possesses superconductivity.