The volume dependence ofT c of ternary A-15 phases

Results are presented of measurements of the superconducting transition temperatureT c , lattice constanta, magnetic susceptibility χ, and critical fieldH c2 for many Nb3Al and V3Si-based ternary phases and Nb3SnH x . For V3Si-based ternary systems and Nb3SnHx the density of states at the Fermi levelN(eF) sharply decreases with the concentration of the alloying element. The variation ofN(eF) in these ternary systems cannot be explained by the variation ofa. In ternary phases Nb3(Al1−xY x ), where Y can be Ge, Ga, Sb, or Se, a quite clear correlation is revealed betweenT c anda. The dependence ofT c onV in these systems is due to the variation of the matrix element of the electron-phonon interaction 〈I2〉.