Electronic structure, lattice stability, and superconductivity of CrC

Electronic-structure and total-energy calculations are used to elucidate the properties of the recently synthesized NaCl-structure CrC phase. The lattice parameter, elastic constants, Γ-point optic-phonon frequency, and formation energy are determined using total-energy methods. No sign of lattice instabilities is found, indicating that NaCl-structure CrC is a true metastable phase. In fact, the elastic constants and optic-phonon frequency have values comparable to those in other known NaCl-structure transition-metal carbides. On the other hand, and in contrast to VC and NbC, CrC is found to be unstable with respect to phase separation into C and Cr, explaining the difficulty of its synthesis. The electronic structure is qualitatively similar to that of TiC and VC except for the placement of the Fermi level ${\mathit{E}}_{\mathit{F}}$. A relatively high density of states at ${\mathit{E}}_{\mathit{F}}$, which is derived from weakly hybridized Cr d states, is found. However, fixed-spin-moment calculations show that this does not lead to a ferromagnetic instability. Rigid muffin-tin approximation electron-phonon-interaction calculations lead to a prediction that CrC is a superconductor with a transition temperature in the range 5–10 K.