Possible thermodynamic stability and superconductivity of antifluorite Be2BxC1-x

The Be(2)B(x)C(1-x) alloy in the antifluorite structure is theoretically studied as a possible superconductor. Although both Be(2)B and Be(2)C terminal phases are experimentally observed to be thermodynamically stable, our calculations suggest that the stability of the Be(2)B phase requires a high concentration of defects. The carbon-rich limit is expected to contain few defects and we predict the alloy to be thermodynamically accessible in the range 0 <= x <= 0.25. The superconducting T(c) is predicted to increase with boron concentration with a value of 3-8 K at x=0.25 and a plateau of 5-13 K for x > 0.4. The uncertainty in this prediction results from a small electron-phonon coupling of lambda <= 0.5 over the entire range of boron concentration. The material remains in the weak-coupling regime of superconductivity where T(c) is sensitive to small variations in lambda and mu*.