Effect of melting temperature on the decomposition and reformation behavior of (Bi, Pb)-2223 core in the Ag-sheathed tape

The effect of melting temperature on the decomposition and reformation of (Bi, Pb)-2223 (abbreviated as 2223) phase in a Ag-sheathed mono-filamentary tape under 7.5%O₂ flow balanced with argon have been investigated by means of ex-situ X-ray diffraction (XRD) and scanning electron microscopy equipped with energy dispersive spectroscopy (SEM/EDS). It is shown that a partial melting at an appropriate temperature range, which produce a 2212-like melt and alkaline earth cuprates (AEC), especially (Sr, Ca)₁₄Cu₂₄O₄₁ (14:24-AEC) and (Ca, Sr)₂CuO₃(2:1-AEC), as the main decomposition products of 2223, is very important for this high-T_c phase reformation. The melt composition evolved from that between 2223 and 2212 stoichiometries towards 2212, and then to 2201 stoichiometry as melting temperature increasing. It is demonstrated that 2223 could be easily formed from a 2212-like melt but Bi-2212 could be crystallized from a near 2201-like melt. The recrystallization of 2223 from the melt at an excessively high temperature might experience two different routes during the slow-cooling, one is that 2223 reformed directly from the melt and the other is that 2223 is transferred from the Bi-2212.