Effect of Ag on the primary phase field of the high- T c (Bi,Pb)-2223 superconductor
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Effect of Ag on the primary phase field of the high-Tc (Bi,Pb)-2223 superconductor W. Wong-Ng and L.P. Cook Ceramics Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
W. Greenwood University of Maryland, College Park, Maryland 20742
A. Kearsley Mathematical and Computational Science Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (Received 30 July 1999; accepted 1 December 1999)
The subsolidus equilibria and the primary phase field (crystallization field) of the 110 K high-Tc (Bi,Pb)-2223 ([Bi,Pb]:Sr:Ca:Cu) phase have been determined in the presence of Ag under a 92.5% Ar/7.5% O2 atmosphere (volume fraction). A total of 29 six-phase volumes that include both the (Bi,Pb)-2223 and Ag phases was observed. These subsolidus volumes are similar to those observed without the presence of Ag. The compositional range of initial melts of these volumes (mole fraction basis) covers BiO1.5 from 5.6% to 25.3%, PbO from 0.4% to 13.8%, SrO from 8.4% to 31.9%, CaO from 12.2% to 33.3%, CuO from 21.7% to 40.9%, and AgO0.5 from 1.2% to 6.3%. Based on these data, the primary crystallization field for the (Bi,Pb)-2223 phase in the presence of Ag was constructed using the convex hull technique. A section through this “volume” was portrayed by holding the AgO0.5, SrO, and CaO components at the median value of the 29 compositions while allowing projection on the other three axes (BiO1.5, PbO, and CuO). The net effect of Ag on the melt composition is a reduction in the PbO concentration and an increase in the SrO content. Applications of the liquidus data are also discussed.
I. INTRODUCTION
In recent years, extensive research and development efforts have been focused on the commercial applications of the 80 K high-Tc superconductor 2212 phase in the Bi–Sr–Ca–Cu–O system, and on the 110 K high-Tc superconductor (Bi,Pb)-2223 phase in the (Bi,Pb)–Sr–Ca– Cu–O (BSCCO) system. These applications include transmission cables, motors, generators, transformers, magnets, fault current limiters, and energy storage systems. One of the obstacles that prevents large-scale commercial application of these high-Tc products is the cost of production. In order to realize the full commercial potential, the performance of the superconductor components, which is closely related to cost, must be optimized. The BSCCO high-Tc components are largely prepared in wire or tape form using powder-in-tube (PIT),1–3 or the powder/wire-in-tube (PWIT)4 methods. The PIT technique involves a multistep process of filling silver tubing with high-Tc superconductor BSCCO powder, followed by repeated packing, cold drawing, rolling, and thermal processing. The PWIT tapes are developed by packing both powder and wires into a silver tube. Grain alignment in both methods is frequently achieved be296
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J. Mater. Res., Vol. 15, No. 2, Feb 2000 Downloaded: 25 Mar 2015
cause of the presence of liquid. The resulting products often show si
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