STABILITY OF HIGH-TC PHASE IN AG-CLAD BI-BASED SUPERCONDUCTING WIRES

The phase stability of the oxide core in Ag-sheathed Bi(Pb)-Sr-Ca-Cu-O superconducting wires was studied by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that the high-T(c) phase (Bi, Pb)2Sr2Ca2Cu3Oy (2223) was very sensitive to the melting temperature and duration of melt processing. When the melting temperature was above 859-degrees-C, the (2223) phase was completely decomposed into low-T(c) (Bi, Pb)2Sr2Cau2Oy (2212) phase; (2223) and (2212) phases co-existed at temperatures between 854-degrees-C and 858-degrees-C, and the (2223) phase remained unchanged at temperatures below 853-degrees-C. The experimental results also revealed that the (2223) phase can be fully recovered with a post-annealing after a short-period melt processing. However, the recovery of (2223) phase cannot be achieved for the samples with long-period melt treatment. The partially melted tapes have higher density, excellent grain alignment and improved H-J(c) property, compared to those without melt treatment.