High-Performance YBCO-Coated Superconductor Wires
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High-Performance YBCO-Coated Superconductor Wires
M. Parans Paranthaman and Teruo Izumi, Guest Editors Abstract This issue of MRS Bulletin provides an overview of the current status of research and development in the area of high-temperature superconductor (HTS) wires. High-temperature oxide superconductors, discovered in the late 1980s, are moving into the second generation of their development. The first generation relied on bismuth strontium calcium copper oxide, and the second generation is based on yttrium barium copper oxide, which has the potential to be less expensive and to perform better. The potential uses of HTS wires for electric power applications include underground transmission cables, oil-free transformers, superconducting magnetic-energy storage units, fault-current limiters, high-efficiency motors, and compact generators. Wires of 10–100 m in length can now be made, but material and processing issues must be solved before an optimized production scheme can be achieved. This issue covers a range of processing techniques using energetic beams, rolling, and laser and chemical methods to form wires with good superconducting properties. Keywords: coated conductors, high-temperature superconductors, YBCO, YBa2Cu3O7.
Since the discovery of high-temperature superconductors (HTSs) in the late 1980s, notably (Bi,Pb)2Sr2Ca2Cu3O10 (known as BSCCO or 2223) and YBa2Cu3O7 (known as YBCO or Y-123), researchers all around the world have searched for ways to produce affordable flexible conducting wires with high current density. The U.S. Department of Energy’s target price for these conductors is close to the current cost of copper wire at $10/kA m USD. The strategic goal is to achieve HTS wire with a current capacity 100 times that of copper. Robust, high-performance HTS wire would certainly revolutionize the electric power grid and various other electric power applications as well. One company, American Superconductor Corp. (AMSC), has been widely recognized as a world leader in manufacturing first-generation (1G) HTS wires based on BSCCO materials using the oxide-powder-in-tube (OPIT) process. AMSC has achieved electrical criti-
MRS BULLETIN/AUGUST 2004
cal current (Ic), defined as the maximum current a superconductor can transport, of more than 125 A/cm-width in piece lengths of several hundred meters, and a “champion” current (the highest current achieved to date for this superconductor) of 170 A at 77 K and self-field in a wire at the standard 4.1 mm width and 210 m thickness.1 However, due to the higher cost—approximately $300/kA m—of 1G wire, researchers worldwide shifted their efforts toward the development of second-generation (2G) YBCO wires. One of the main obstacles to the manufacture of commercial lengths of YBCO wire has been the phenomenon of weak links: grain boundaries formed by the misalignment of neighboring YBCO grains are known to form obstacles to current flow. By carefully aligning the grains, low-angle boundaries between superconducting YBCO grains allow more current to flow. In f
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