Influence of Pb-rich phases of precursor powder on microstructural evolution in the silver-sheathed (Bi,Pb)2Sr2Ca2Cu3Ox superconducting tapes

The influence of Pb-rich phases of precursor powder on microstructural evolution during the first heat treatment of the silver-sheathed (Bi,Pb)2Sr2Ca2Cu3Ox ((Bi,Pb)-2223/Ag) superconducting tapes was studied by means of in situ synchrotron X-ray diffraction. Three monofilament tapes were fabricated using precursor powders containing different Pb-rich phases.

Sintering was carried out at a fixed temperature of 830 °C in 8.5% O2. The phase transitions, structure changes and texture evolution in (Bi,Pb)-2223/Ag tapes were carefully analyzed, and the evolution of different Pb-rich phases, such as Ca2PbO4 and Pb3Sr2.5Bi0.5Ca2CuOy (3321), was discussed. It was found that tapes fabricated using the precursor with the (Bi,Pb)-2212 phase exhibited higher (Bi,Pb)-2223 formation rate than tapes fabricated using the precursors with Pb-rich phases.

Texture evolution indicates that texture of the (Bi,Pb)-2212 phase formed in the thermomechanical process depends strongly on the Pb-rich phases of the precursor powders, while the texture of the new formed (Bi,Pb)-2223 grains for all three tapes follows the texture of (Bi,Pb)-2212 grains, and the final (Bi,Pb)-2223 and (Bi,Pb)-2212 textures are approximately identical.

A higher texture degree of (Bi,Pb)-2223 grains was achieved in tapes fabricated using the precursors with 3321 or Ca2PbO4 phases.