Hole-doped, High-Temperature Superconductors Li_(x)BC, Na_(x)BC and C_(x) : A Coherent-Potential-Based Prediction

Using density-functional-based methods, we show that the hole-doped Li_{x}BC and Na_{x}BC in P6_{3}/mmc crystal structure and C_{x} in graphite structure are capable of showing superconductivity, possibly with a T_{c} much higher than that of MgB_{2}. We use full-potential methods to obtain the optimized lattice constants a and c, coherent-potential approximation to describe the effects of disorder, Gaspari-Gyorffy formalism to obtain the electron-phonon coupling constant $\lambda$, and Allen-Dynes equation to calculate T_{c} as a function of hole concentration in these alloys.