The effect of lead content on the critical current density, irreversibility field, and microstructure of Ag-clad Bi 1.8
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The effect of lead content on the critical current density, irreversibility field, and microstructure of Ag-clad Bi1.8 Pbx Sr2 Ca2 Cu3 Oy tapes J. W. Andersona) Applied Superconductivity Center and Materials Science Program, University of Wisconsin-Madison, 1500 Engineering Drive, Madison, Wisconsin 53706
S. E. Dorris Energy Technology Division, Argonne National Laboratory, Argonne, Illinois 60439
J. A. Parrellb) and D. C. Larbalestier Applied Superconductivity Center and Materials Science Program, University of Wisconsin-Madison, 1500 Engineering Drive, Madison, Wisconsin 53706 (Received 6 November 1997; accepted 7 June 1998)
We studied the effect of lead content (x 0.20–0.40) on the critical current density Jc (0 T, 77 K), irreversibility field H p (77 K), and microstructure of monocore, Ag-clad Bi1.8 Pbx Sr2 Ca2 Cu3 Oy (2223) tapes, finding that tapes with lower lead contents (x 0.20–0.25) required higher processing temperatures (840 and 832 ±C, respectively) to complete 2223 formation, as compared to the optimum 820 ±C reaction temperature of the x 0.30–0.40 tapes. We found that both the zero-field and the in-field properties correlated strongly to the phase purity with Jc (0 T, 77 K) reaching a maximum of ,20 kAycm2 for x 0.30, and then decreasing with increasing lead content to ,12 kAycm2 for x 0.40. H p (77 K) increased from ,165 mT at x 0.20 to ,265 mT at x 0.30, then declined to 195 mT at x 0.40. Optimizing the lead content at x 0.30 maximized both the connectivity and the flux pinning contributions to the critical current density.
I. INTRODUCTION 1
After Sunshine et al. discovered that lead-doping promotes formation of the high Tc (110 K) (Bi, Pb)2 Sr2 Ca2 Cu3 Ox (2223) phase, partial lead substitution for bismuth became widely accepted as a method to form nearly phase-pure 2223. Adding lead to Bi2 Sr2 Ca1 Cu2 Oy (2212) results in a tetragonal-to-orthorhombic structural transformation2 and a decrease in melting temperature.3,4 Furthermore, lead promotes the formation of a transient liquid phase5–17 which is beneficial in increasing the kinetics and extent of the reaction to 2223,18–22 while also healing cracks that are formed in the Ag-sheathed tapes during mechanical processing.23–26 In addition to increasing the phase purity and reaction kinetics, lead also positively influences the superconducting properties, as is clearly evidenced by its effect on the properties of lead-doped 2212 single crystals. Several authors27–30 reported that lead doping rea)
Present address: Motorola, 3501 Ed Bluestein Blvd., Austin, Texas 78721. b) Present address: Oxford Superconducting Technology, 600 Milik Street, Carteret, New Jersey 07008. 340
http://journals.cambridge.org
J. Mater. Res., Vol. 14, No. 2, Feb 1999
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duces both the ab plane and c-axis resistivity, as well as the electromagnetic anisotropy, thereby improving the flux pinning at low temperatures, and extending the irreversible domain of finite Jc to higher temperat
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