New approach to depositing yttria-stabilized zirconia buffer layers for coated conductors
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B.W. Kang and A. Goyal Metals and Ceramics Division, Oak Ridge National Laboratory, P.O. Box 2008, MS 6116, Oak Ridge, Tennessee 37831-6116
P.N. Barnes and C.E. Oberly Propulsion Directorate, U.S. Air Force Research Laboratory/PRPG, Building 450, 2645 Fifth Street, Suite 13, Wright-Patterson Air Force Base, Ohio 45433-7919 (Received 19 September 2002; accepted 14 January 2003)
A new approach for the production of yttria-stabilized zirconia (YSZ) oxide buffer layers directly on metal rolling-assisted biaxially textured substrates (RABiTS) is described in this paper. This represents a significant advance over existing techniques and avoids the need for complicated steps to avoid substrate oxidation during direct deposition of oxides. Current densities of about 1 MA/cm2 have been achieved for YBa2Cu3O7−␦ layers on the YSZ buffer, with an intermediate CeO2 layer. The process consists of reactive sputtering of a YxZr1−xN film directly on the RABiTS, which adopts its biaxial texture. This nitride film is then converted to YSZ via a thermal oxidation step. The YSZ films retain the texture of the nitride film (and of the RABiTS) through local syntaxy. In many cases, YSZ films exhibit improved biaxial texture over that of the RABiTS substrate. Nitrides can be sputter deposited at much higher rates relative to oxides, making the approach industrially scalable and economical.
I. INTRODUCTION
High-temperature superconductor (HTS)-coated conductors represent the next generation of HTS wire technology, with primary application in power generation, power transmission, and compact motors for both commercial and military use. HTS tapes, formed by HTS deposition onto buffered, biaxially textured metal substrate tapes, are intended to replace copper as a conductor in these applications. Cold-rolled and annealed nickel can yield tapes with strong biaxial texture, called rollingassisted biaxially textured substrates (RABiTS).1–4 YBa2Cu3O7−␦ (YBCO) cannot be deposited directly onto the tapes due to tape oxidation and chemical interdiffusion issues,5 so buffer layers must be used. The buffers act as a chemical diffusion barrier, adopt the biaxial texture of the tape, and provide a surface upon which (001) biaxially textured YBCO can be deposited. Control of the biaxial texture of the final YBCO superconducting layer is critical to the success of the YBCO-coated conductor. a)
Address all correspondence to this author. e-mail: [email protected] b) Present address: Functional Coating Technology, LLC, 1801 Maple Avenue, Evanston, IL 60201. J. Mater. Res., Vol. 18, No. 4, Apr 2003
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Misorientation at YBCO grain boundaries, both [100]-tilt and [100]-twist, have a significant impact on critical current density (Jc); nearly an order-of-magnitude drop in intergrain critical current densities is observed between 5° and 10° of [100] misorientation.6–8 Theoretical calculations show that the maximum reduction in Jc in going from a short sample to a kilometer length is only 10–20% for the ty
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