Conductors with controlled grain boundaries: An approach to the next generation, high temperature superconducting wire
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Conductors with controlled grain boundaries: An approach to the next generation, high temperature superconducting wire A. Goyal Metals & Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6116
D. P. Norton Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6116
D. M. Kroeger Metals & Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6116
D. K. Christen Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6116
M. Paranthaman Chemistry and Analytical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6116
E. D. Specht Metals & Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6116
J. D. Budai Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6116
Q. He and B. Saffian University of Tennessee, Knoxville, Tennessee 37996-1200
F. A. List, D. F. Lee, E. Hatfield, P. M. Martin Metals & Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6116
C. E. Klabunde Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6116
J. Mathis and C. Park Oak Ridge Institute of Science and Education, Oak Ridge, Tennessee 37831 (Received 29 April 1997; accepted 25 June 1997)
Much of the conductor development effort in the last decade has focused on optimizing the processing of (Bi, Pb)2 Sr2 Ca2 Cu3 Ox oxide-powder-in-tube conductors and (Bi, Pb)2 Sr2 CaCu2 O8 (Bi-2212) and TlBa2 Ca2 Cu3 Ox thick film conductors. It is demonstrated that in each of these conductors, critical current densities are dictated by the grain boundary misorientation distributions (GBMD’s). Percolative networks of low-angle boundaries with fractions consistent with the active cross-sectional area of the conductor exist in each of these conductors. Further enhancements in the properties require increased numbers of small-angle grain boundaries. Given the processing methods used to fabricate these materials, no clear route employing a simple modification of the established processing method is apparent. To address this need, conductors with controlled or predetermined GBMD’s are necessary. Development of biaxial texture appears to be the only possible way to increase the number of small-angle boundaries in a practical and controllable manner. We summarize in this paper recent results obtained on epitaxial superconducting films on rolling-assisted-biaxially-textured-substrates (RABiTS). This technique uses well established, industrially scalable, thermomechanical processes to impart a strong biaxial texture to a base metal. This is followed by vapor deposition of epitaxial buffer layers (metal and/or ceramic) to yield structurally and chemically compatible surfaces. Epitaxial YBa2 Cu3 O7–d films grown using laser ablation on such substrates have critical current densities exceeding 106 Aycm2 at 77 K in zero field and have a field dependence similar to epitaxial films on single cry
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