Second critical magnetic field of superconducting BaPb/sub 1-x/Bi/sub x/O/sub 3/ ceramics

The results of an investigation of the conductivity of ceramic BaPb/sub 1-x/Bi/sub x/O/sub 3/ samples with compositions in the range 0.05< or =x< or =0.30, carried out at temperatures above 1.15 K in magnetic fields up to 200 kOe, were used to determine the second critical magnetic field as a function of temperature. In all cases the results of measurements disagreed with a theoretical curve predicted in the dirty limit for type II superconductors. An analysis was made of the relationship between this discrepancy and the characteristic features of conduction with carrier localization in BaPb/sub 1-x/Bi/sub x/O/sub 3/.