Effect of copper (II) sulfide addition on the transport critical current density and AC susceptibility of Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O₁₀ superconductor

The effect of copper (II) sulfide (CuS) addition on the superconductivity of (Bi_1.6Pb_0.4)Sr₂Ca₂Cu₃O₁₀ (CuS)_x (x = 0–1.5 wt%) is reported. All samples were prepared via the co-precipitation technique. The XRD patterns revealed that the formation of Bi-2223 phase was not affected by the CuS addition. The temperature-dependent resistance measurements showed a metallic normal state behavior for all samples, with onset transition temperatures T_{c onset} between 109 and 118 K and zero transition temperatures T_{c zero} between 96 and 101 K. The intragranular and intergranular diamagnetic transition, intrinsic and coupling peak temperatures, the onset temperature of grain decoupling and the Josephson phase-locking temperature of (Bi_1.6Pb_0.4)Sr₂Ca₂Cu₃O₁₀ were not suppressed at lower CuS additions (x ≤ 0.2 wt%) but further CuS additions (x = 0.8–1.5 wt%) severely suppressed these properties. The highest Josephson current (10.82 μA) and Josephson energy coupling (22.22 meV) were exhibited by the non-added sample. The volume fraction of the grains decreased when CuS was added which indicated that the intergranular contribution was enhanced as shown by the AC susceptibility curves for all added samples. The highest transport critical current density, J_ct at 40 K was for x = 0.2 wt% sample (4713 mA cm⁻²). The effect of internal lattice strain on the transition temperatures was also discussed. This work showed that lower addition of CuS could enhance the connectivity between the grains and enhance flux pinning.