BaC: a thermodynamically stable layered superconductor

Abstract

To predict all stable compounds in the Ba–C system, we perform a comprehensive study using first-principles variable-composition evolutionary algorithm USPEX. We find that at 0 K the well-known compound BaC₂ is metastable in the whole pressure range 0–40 GPa, while intercalated graphite phase BaC₆ is stable at 0–19 GPa. A hitherto unknown layered orthorhombic Pbam phase of BaC has structure consisting of alternating layers of Ba atoms and layers of stoichiometry Ba₂C₃ containing linear C₃ groups and is predicted to be stable in the pressure range 3–32 GPa. From our electron–phonon coupling calculations, the newly found BaC compound is a phonon-mediated superconductor and has a critical superconductivity temperature T_c of 4.32 K at 5 GPa. This compound is dynamically stable at 0 GPa and therefore may be quenchable under normal conditions.