Hole-doped, high-temperature superconductors LixBC, NaxBC and Cx: a coherent-potential-based prediction

Using density-functional-based methods, we show that the hole-doped LixBC and NaxBC in P63/mmc crystal structure and Cx in graphite structure are capable of showing superconductivity, possibly with a Tc much higher than that of MgB2. We use the pseudopotential method to obtain the optimized lattice constants a and c, the coherent-potential approximation to describe the effects of disorder, the Gaspari–Gyorffy formalism to obtain the electron–phonon coupling constant λ, and the Allen–Dynes equation to calculate Tc as a function of hole concentration in these alloys.