Improvement of Bi-2223/Ag tape performances through the control of the Pb-rich phases present in the precursors powders

Precursor powders containing different lead-rich phases: (a) Ca2PbO4, (b) Pb-3(Sr,Bi)(3)Ca2CuOy (3321), were prepared by controlling the calcination temperature and atmosphere. Monofilament tapes were fabricated using those two powders. It has been found that both the microstructure and critical current depended strongly on the nature of the lead-rich phase. Tapes fabricated using the precursor with the Ca2PbO4 phase (tape T1) had a much lower optimum sintering temperature and a narrower temperature window than tapes fabricated using the precursor with the 3321 phase (tape T2). The critical current density J(c), of tape T2 is improved by a factor 1.5-2. SEM results show that a large fraction of secondary phases with big particle size was formed in the fully reacted tape TI, which might degrade the critical current of these tapes. On the contrary, little and small secondary phases were formed in tape T2. It can be concluded that the control of the lead-rich phases present in the precursors is an effective way to improve the Jc values. The improvement in J(c) of tape T2 is related to the improved grain connectivity, better texture of (Bi,Pb)(2)Sr2Ca2Cu3Ox grains as well as increased phase purity. (C) 2004 Elsevier B.V. All rights reserved.