Superconductivity in A15 compounds (Vsub(1-x)Msub(x))3Ge with M = Ti, Cr, Mn, Zr and Mo

Superconductivity has been studied through resistivity measurements on the A15 systems (Vsub(1-x)Msub(x))3Ge with M = Ti, Cr, Mn, Zr and Mo. An increase of concentration x in all the systems causes a monotonic decrease of the transition temperature Tsub(c), while the residual resistivity rho0 rises. An increase of the V site disorder due to alloying, which is indicated by the rise of rho0, is accompanied by a monotonic decrease of the electron-phonon resistivity rhosub(ep)(300K). The electron-phonon parameters, lambda and lambdasub(tr), deduced from the experimental result are expressed as universal functions of the electron-atom ratio e/a. A deviation of e/a from 4.75 due to alloying lowers both lambda and lambdasub(tr), which is in contrast with the recent prediction based on the rigid-band model. (author)