Vortex phase diagram and transition in (Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10-δ)_1-x(SnO₂)_x superconductors

The superconducting vortex phase diagram of (Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10-δ)_1-x(SnO₂)_x ceramics, where x = 0, 0.002, 0.004, 0.006, 0.008, and 0.010, was investigated using resistivity measurement under magnetic fields. If the value of the offset critical temperature (T_c,offset) monotonously decreased on the SnO₂-added samples, then the mean-field critical temperature (T_mf) would slightly improve on the x = 0.002 sample. The excess conductivity of all samples was analyzed based on the Aslamazov–Larkin and Lawrence–Doniach models. The c-axis coherence length at 0 K (ξ_c(0)) and the interlayer coupling strength were optimized on the x = 0.002 sample. The activation energy (U₀) calculated using the Arrhenius model was also increased, and the maximum for the x = 0.002 sample was reached. The upper critical field (B_c2) deduced using the Werthamer–Helfand–Hohenberg model was also enhanced for the x = 0.002 sample. The small bundle field (B_sb), large bundle field (B_lb), irreversibility field (B_irr), and B_c2 were combined for the vortex phase (B-T) diagram of the x = 0.000 and x = 0.002 samples. All pinning regimes of the x = 0.002 sample were extended, clearly revealing the improvements in the flux pinning properties in that sample.