Specific Heat and Superconductivity in BaPb_1−xBi_xO₃

Abstract

Specific heat coefficient of BaPb_1−xBi_xO₃ 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⁻¹K⁻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.