We have evaluated the effect of bending strain on the critical current of Bi-2223/Ag tapes with different structures. The measured results were analysed using a symmetric pure bending model. The irreversible degradation indicates that the Ic reduction is caused mainly by crack formation and propagation in the brittle Bi-2223 ceramic core. Experimented results have shown that the number of filaments, as well as the structure of the tapes, could have strong effects on the measured apparent critical values of the tapes. Multifilamentary tapes showed better performance compared with single core tapes. The bending strain tolerance of the tape could be improved by adding a metal strip on the upper side of the tape.

The microstructural evolution of Bi-2223/Ag tapes during cooling after the first heat treatment is investigated by SEM, XRD and EDS. Cooling was carried out after samples were heat treated at 840 °C for 10 h. Samples were quenched in air from different temperatures during the cooling process. Investigation showed that the volume fraction of Bi-2223 increased during the initial stages of cooling, reaching a maximum of 93% at 780 °C, and then began to decrease as the temperature fell below 780 °C. CuO particles precipitated out from the liquid phase and grew into big particles at temperatures below 750 °C. The Ca2PbO4 phase formed rapidly at the beginning of the cooling process, while the 3321 phase began to form only below 750 °C. The formation and amount of the lead-rich phases are associated with the amount of the liquid present at high temperatures.

The phase evolution of lead oxide compounds in (Bi,Pb)2Sr2Ca2Cu3Ox (BSCCO) precursor powder during heat treatment was studied. The BSCCO powder oxygen release and absorption processes occurring during heat treatment were investigated by using an oxygen analyser. The experimental results show that the oxygen release and absorption processes are related to evolution of the lead oxide compounds in the BSCCO powder. Oxygen absorption may result from the segregation of Pb from the (Bi,Pb)-2212 phase as well as the formation of the Pb3Sr2.5Bi0.5Ca2CuOy (3321) and Ca2PbO4 phases. Oxygen release could be related to decomposition of the 3321 and Ca2PbO4 phases as well as incorporation of Pb into the (Bi,Pb)-2212 phase. The formation and decomposition of the 3321 and Ca2PbO4 phases, which depend on temperature and oxygen partial pressure, have also been identified.