The influence of post-annealing on the Pb₃(Bi_0.5Sr_2.5)Ca₂CuO_y phase evolution and superconducting properties of (Bi,Pb)-2223/Ag tapes

Post-annealing (PA) at reduced oxygen atmosphere was proved to be quite effective for increasing the critical current (I_c) of (Bi,Pb)-2223/Ag superconducting tapes. In this work, PA was performed at various oxygen partial pressure (pO₂ = 0.01-0.50 bar). The dwelling temperature was chosen in the region of 700-840 °C with respect to pO₂. It was found from XRD patterns that the Pb₃(Bi_0.5Sr_2.5)Ca₂CuO_y (3321) phase appeared after PA, whose amount changed with pO₂ and PA temperature. I_c can be increased by up to 24% if pO₂ < 0.20 bar. The optimum window for achieving high I_c values became wider at lower pO₂. The critical temperature (T_c) was also changed after PA. An optimum 3321 phase content was found to be related to the maximum T_c.