Phase evolution during post-annealing and its influence on critical currents of (Bi,Pb)-2223/Ag tapes

Post-annealing (PA) has been performed on fully reacted multifilamentary (Bi,Pb)-2223/Ag tapes in 8.5% O2 atmosphere. The tapes were sintered within 770-800 °C for 10 h and at 795 °C for 5-50 h. The measurements showed that Ic (77 K,SF) was increased by 12-19% after PA within 790-800 °C. It was found by means of XRD that the Pb3(Bi0.5Sr2.5)Ca2CuOx (3321) phase appeared after PA, its amount decreasing with increasing PA temperature. There was an optimum 3321 content to achieve the maximum Ic. Tc was increased by PA, and then decreased with increasing temperature. The field dependent Ic and n value measurements performed at 4.2 K, 10 K, 30 K and 77 K suggested that PA improves grain connectivity and collective flux pinning.