Study on the evolution of superconducting phases during the decomposition and recrystallization of (Bi,Pb)-2223 phase in the Ag-sheathed tape

The evolution relationship among the three well-known superconducting phases in BPSCCO system, Bi-2223, Bi-2201 and Bi-2212, has been investigated after the Bi-2223 core in a Ag-sheathed monofilamentary tape was melted decomposed at different maximum temperatures (T_p), followed by slow cooling down to the end temperatures in a Ar-7.5%O₂ flowing atmosphere. The fractions of Bi-2223 decomposition and Bi-2201 increased with T_p rising from 855 °C to 865 °C. The decomposition products in the short tapes partially melted at quenched from T_p = 855°C~860°C are Bi-2201, 2:1 AEC and 14:24 AEC etc. During cooling at 0.025°C / min, Bi-2223 phase partially decomposed was fully reformed directly from the melt. No Bi-2212 was found in the specimens which were heated to 855°C-865 °C and slowly cooled after melted at 855°C~860°C. The results above mentioned indicate that the Bi-2223 phase can be formed directly from the melt. However, after fully decomposed at 865°C, Bi-2223 phase reformation seems to include two routes at the same cooling rate: a small quantity of this phase recrystallizes from the melt. Bi-2223 is transferred from Bi-2212 which firstly formed from the melt during the subsequent slow-cooling.