Effects of C, Cu, and Be substitutions in superconducting MgB2 -: art. no. 140509

Density functional calculations are used to investigate the effects of partial substitutional alloying of the B site in MgB2 with C and Be alone and combined with substitution of Mg by Cu. The effect of such substitutions on the electronic structure, electron-phonon coupling, and superconductivity are discussed. We find that Be substitution for B is unfavorable for superconductivity as it leads to a softer lattice and weaker electron-phonon couplings. Replacement of Mg by Cu increases the lattice stiffness and electron count. We estimate that with full replacement of Mg by Cu and fractional substitution of B by C, T-c values of 50 K may be attainable.