Fabrication and Characterization of High-Temperature Superconducting \({Bi_{2-x}Pb_xSr_2Ca_2Cu_3O_{10+\gamma}}\) Tapes

This work reports the fabrication and comprehensive characterization of \({Bi_{2-x}Pb_xSr_2Ca_2Cu_3O_{10+\gamma}}\) superconducting tapes with coexistence of Pb-doped Bi-2223 and Bi-2212 phases, embedded in a high-purity silver matrix. The tapes were produced by the powder-in-tube (PIT) method, followed by heat treatments at 865 and 810 °C and mechanical lamination, yielding homogeneous tapes with a thickness of about 0.6 mm. Structural analysis by X-ray diffraction shows that the precursor powder consists mainly of the BPSCCO-2223 phase and a carbonate secondary phase, whereas the tape core additionally contains the BPSCCO-2212 phase, \({Ca_2PbO_4}\) and \({Ca_{2.675}Cu_3Pb_{0.535}Sr_{2.675}Bi_{1.6}O_x}\). SEM-EDS confirms the flattening and alignment of grains after rolling, the presence of Ca- and Pb-rich secondary phases, and the absence of detectable silver diffusion into the core. DC susceptibility measurements under 50 and 1000 Oe reveal two superconducting transitions in the core, associated with the 2223 and 2212 phases, and a clear reduction of the irreversibility temperature with respect to the powder. From hysteresis loops, the critical fields (\({H_{C1}}\) and \({H_{irr}}\)) and the vortex-matter \(B-T\) phase diagrams were constructed, showing a shift of the irreversibility line to lower fields and temperatures for the tape core. The critical current density estimated with the Bean model reaches values of the order of \({10^5\ A/cm^2}\) at 10 K for the tape core, with the enhancement attributed to grain alignment and secondary-phase pinning. Magnetic relaxation measurements show a complex, two-plateau decay in the core at 5 K, attributed to the competition between the coexisting 2223 and 2212 phases. The results provide a complete picture of the microstructural, magnetic and transport behaviour of Pb-doped Bi-2223 tapes and establish a basis for their optimisation.