Influence of the Oxygen Partial Pressure on the Phase Evolution During Bi-2212 Wire Melt Processing

• Published in: IEEE transactions on applied superconductivity 2016-04, Vol.26 (3), p.1-4
• Main Authors: Scheuerlein, C., Andrieux, J., Rikel, M. O., Kadar, J., Doerrer, C., Di Michiel, M., Ballarino, A., Bottura, L., Jiang, J., Kametani, F., Hellstrom, E. E., Larbalestier, D. C.
• Format: Article
• Language: English
• Subjects: Bi-2212; Chemical Sciences; Condensed Matter; Diffraction; Heating; Material chemistry; Materials Science; melt processing; Physics; Superconductivity; Synchrotrons; Temperature measurement; Wires; X-ray diffraction; X-ray scattering; XRD
• ISSN: 1051-8223; 1558-2515
• DOI: 10.1109/TASC.2016.2533574

We have studied the influence of the oxygen partial pressure pO 2 up to 5.5 bar on the phase changes that occur during the melt processing of a state-of-the-art Bi-2212 multifilamentary wire. Phase changes have been monitored in situ by high energy synchrotron X-ray diffraction. We found that the stability of the Bi-2212 phase is reduced with increasing pO 2 . For pO 2 > 1 bar, a significant amount of the Bi-2212 phase decomposes upon heating in the range of 400 °C-650 °C. The extent of decomposition strongly increases with increasing pO 2 , and at pO 2 = 5.5 bar Bi-2212 completely decomposes in the solid state. Textured Bi-2212 can be formed during solidification when pO 2 is reduced to 0.45 bar when the precursor is molten. Since the formation of current-limiting second phases is very sensitive to pO 2 when it exceeds 1 bar, we recommend to reduce the oxygen partial pressure below the commonly used pO 2 = 1 bar, in order to increase the pO 2 margins and to make the overpressure process more robust.