Preparation of (Bi, Pb)-2223/Ag tapes by high temperature sintering and post-annealing process

Abstract A novel heat treatment process was developed to fabricate (Bi, Pb)-2223/Ag tapes with high critical current density ( J c ). The process can be divided into two parts: reformation and post-annealing. Tapes were first heated to the maximum temperature (830–860 °C) followed by slow cooling (reformation). Then, tapes were annealed between 760 and 820 °C (post-annealing). Reformation is expected to produce a large amount of liquid phase which may heal microcracks, decrease porosity, and improve grain growth. However, since the sintering temperature is beyond the Bi-2223 single-phase region, much Bi-2212 and secondary phases will appear at the Bi-2223 grain boundaries. During post-annealing, these phases may convert to (Bi, Pb)-2212 and even to Bi-2223. Hence, the J c values for these tapes are significantly improved. The microstructure and the phase composition were investigated by high-energy synchrotron XRD and SEM/EDX. Some process parameters e.g. sintering temperature, cooling rate, and post-annealing time were optimised.