Influence of powder pre-annealing on the phase formation and critical current of Bi-2223/Ag tapes

The influence of precursor powders with different lead-rich phases, such as Ca2PbO4 and Pb-3(Sr,Bi)(3)Ca2CuOy (3 3 2 1), on the phase formation and critical current of Bi-2223/Ag tapes has been studied. Three precursors with different phase assemblages were prepared and used to make the tapes. The effects of different precursors were investigated by XRD, SEM/EDS and critical current measurements. It has been found that both the microstructure and phase formation depended strongly on the different lead-rich phases, which determined the reactivity of the precursor. Tapes fabricated using the precursor with Ca2PbO4 phase (tape T1) had lower transformation rate of 2223 phase than tapes fabricated using the precursor with 3321 phase (tape T2). SEM results show that a large fraction of secondary phases with big particle size was formed in the tape T1 during the subsequent sintering, which might degrade the critical current of the tapes. On the contrary, a small amount of secondary phases with small particle size was formed in the tape T2. Consequently, the critical current of tape T1 was lower than that of tape T2. (C) 2004 Elsevier B.V. All rights reserved.