Specific Heat and Superconductivity in BaPb_1-<i>x</i>Bi_<i>x</i>O₃

Abstract

Specific heat coefficient of BaPb 1- x Bi x O 3 at low temperatures was measured by the thermal relaxation method. Although the discontinuity in the specific heat C at the superconducting transition temperature T c could not be detected, it was clearly observed in the lowest experimental temperature region that C in the superconducting state at zero magnetic field was smaller than in the normal state at H =59 kOe. The electronic specific heat coefficient γ increased with x until x =0.25 and then decreased above, corresponding to the composition dependence of T c . However, the γ value, e.g. 1.6 mJ mole -1 K -2 at x =0.25, was one to two orders of magnitude smaller than those of the other typical high T c superconducting metals. The Debye temperature was in the range 166 K to 196 K for 0 ≤ x ≤0.3.