This article provides an overview of the fabrication of epitaxial, biaxially aligned buffer layers on rolling-assisted biaxially textured substrates (RABiTS) as templates for YBCO films carrying high critical current densities.The RABiTS technique uses standard thermomechanical processing to obtain long lengths of flexible, biaxially oriented substrates with smooth surfaces.The strong biaxial texture of the metal is conferred to the superconductor by the deposition of intermediate metal and/or oxide layers that serve both as a chemical and a structural buffer.Epitaxial YBCO films with critical current densities exceeding 3 106A/cm2at 77K in self-field have been grown on RABiTS using a variety of techniques and demonstrate magnetic-field-dependent critical current values that are similar to those of epitaxial films on single-crystal ceramic substrates.The RABiTS architecture most commonly used consists of a CeO2 (sputtered)/YSZ (sputtered)/Y203 (e-beam)/Ni-W alloy.
The desired texture of the base metal has been achieved in 100 m lengths and 10cm widths.Scaleable and cost-effective techniques are also being pursued to deposit the epitaxial multilayers.The results discussed here demonstrate that this technique is a viable route for the fabrication of long lengths of high-critical-current-density wire capable of carrying high currents in magnetic fields and at temperatures accessible by cooling with relatively inexpensive liquid nitrogen (up through the 77K range).
Amit Goyal is currently task manager and technical leader of Superconducting Materials Research at Oak Ridge National Laboratory. His research interests include grain-boundary design of materials, texture analysis, development and control in metals and ceramics, synthesis of superconductors, deposition of epitaxial metal/alloy and ceramic thin/thick films by physical and chemical vapor deposition, and the development of advanced electronic materials such as superconductors and photovoltaics.
Goyal received a BTech degree in metallurgical engineering from the Indian Institute of Technology in 1986, an MS degree in mechanical and aerospace engineering from the University of Rochester in 1988, and a PhD in materials science and engineering from the University of Rochester in 1991.
Goyal is the lead inventor of the RABiTS process for fabricating high-performance superconducting wires. He holds 39 U.S. patents with 15 more pending, and four international patents with more pending, related to the RABiTS process. He was named a Battelle Distinguished Inventor in 2003. He has received numerous other awards, including a 2003 Exceptional Accomplishment Award from the U.S. Department of Energy, a 2001 Federal Laboratory Consortium Award, a 2001 Energy 100 Award, the 1999 MIT Technical Review TR100 Award, the 1999 ORNL Inventor of the Year Award, a 1999 R&D 100 Award, the 1997 Lockheed-Martin NOVAAward for technical achievement, and the 1996 DOE Materials Science Award for technical achievement in solid-state physics.
Goyal has authored or co-authored over 250 publications and conference proceedings. He has given five plenary talks, more than 90 invited presentations in national and international conferences, and has published over 30 invited papers and book chapters. He has coedited four books on high-temperature superconductivity. His work has received more than 1000 citations from firstand second-author publications alone. He was a member of the advisory board for the Materials Research Science & Engineering Center of Excellence at Carnegie Mellon University during 1999 and 2000. He was a member by invitation on the panel of judges for the 2000, 2001, and 2002 R&D 100 awards. He was a member by invitation on the panel of judges for the 2000 DOE university project peer review as well as a member by invitation on the review panel for DOE, DARPA, and NSF programs. He has been a reviewer for numerous national and international technical journals. He has also organized many symposia and workshops and chaired numerous sessions in national and international conferences.
He was invited to teach/conduct a short course on superconductivity at the University of Talca in Chile in December 2000. He is a principal editor of the Journal of Materials Research and serves on the international advisory board of editors of the Journal of the Korean Institute of Applied Superconductivity and Cryogenics. He is also an associate editor for the Journal of the American Ceramic Society.
Goyal can be reached by e-mail at email@example.com.
M. Parans Paranthaman, Guest Editor for this issue of MRS Bulletin, is a senior research staff member in the Chemical Sciences Division at Oak Ridge National Laboratory. He is also the task manager for hightemperature superconductor chemistry projects at ORNL. He was recently named a distinguished inventor at ORNL by the Battelle Institute of Columbus, Ohio, which partners with the University of Tennessee to form UTBattelle, which manages ORNL for DOE.
Paranthaman is one of the co-inventors of the rolling-assisted biaxally textured substrate (RABiTS) process for fabricating highperformance superconducting wires, which earned an R&D 100 Award in 1999. His present research focus is on the development of coated conductors using vacuum and nonvacuum processing techniques, materials synthesis, and characterization of hightemperature superconductors. He has authored or co-authored more than 230 publications in his area and has over 1500 citations to his work. He has given several invited presentations at national and international conferences. He holds 17 U.S. patents related to the RABiTS technology.
Paranthaman received his PhD degree in materials science and solidstate chemistry from the Indian Institute of Technology Madras in 1988. He was a postdoctoral fellow at the University of Texas Center for Materials Science and Engineering and a research associate in the superconductivity laboratories at the University of Colorado. He joined Oak Ridge National Laboratory in 1993.
He has written several book chapters in the area of superconductivity. He has also edited a book on Materials for High Temperature Superconductor Technologies. He organized the high-temperature superconductivity symposia at the 2001 MRS Fall meeting and the 2004 ACS meeting and has chaired numerous sessions at national and international conferences. He also organized an international workshop on superconductors and applications sponsored by MRS in Gatlinburg, Tenn., in August 2002.
He was a member by invitation on the panel of judges for the 1999, 2000, and 2004 Department of Energy's university project and industry peer reviews. In addition, he has been a member by invitation on the review panels for DOE and DARPA programs.
In 2001, Paranthaman was a member of the group that earned a Federal Laboratory Consortium Award and an Energy 100 Award from DOE. He was with the group that earned the 1997 Lockheed Martin NOVA Award for technical achievement. In 1997, Paranthaman was named Lockheed Martin Scientist of the Year. He has earned numerous other awards during his career at ORNL, which began in 1993. Earlier this year, he was named to the North American editorial board of Superconductor Science and Technology. He is also an associate editor for the Journal of the American Ceramic Society.
Paranthaman can be reached by e-mail at firstname.lastname@example.org.
Urs Schoop is a senior technical staff member at American Superconductor Corporation in Westborough, Mass. His work at AMSC is focused on the research, development, and manufacturing of secondgeneration (2G) coated conductor wire. He leads the research and development effort on epitaxial growth of oxide buffer layers on metal foils and is responsible for scale-up of this technology for the manufacturing of 2G coated conductors. He joined AMSC in 2000.
Schoop received his diploma degree in physics from University of Tübingen, Germany, in 1995 and his PhD degree in physics from the University of Cologne in 2000. In Cologne, his research included processing of YBCO ramp-type junctions and characterization of bicrystal Josephson junctions. He also studied transport characteristics of lowangle grain boundaries in YBCO and other high-temperature superconductors. Throughout his career, he has developed an extensive background on the deposition of epitaxial thin films of ceramic materials by physical vapor deposition methods as well as the characterization of their structure and electric properties.
Schoop can be reached at American Superconductor, 2 Technology Dr., Westborough, MA 01581 USA; tel. 508-621-4366, fax 508-0836-4248, and e-mail email@example.com.