Single Buffer Layer Technology for YBCO Coated Conductors
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Single Buffer Layer Technology for YBCO Coated Conductors M. Parans Paranthaman1 , T. Aytug1 , H.Y. Zhai1 , S. Sathyamurthy1 , H.M. Christen1 , P.M. Martin1 , D.K. Christen1 , R.E. Erickson2 , and C.L. Thomas2 1 Oak Ridge National Laboratory, Oak Ridge, TN 37831-6100, USA 2 3M Company, St. Paul, MN 55144, USA ABSTRACT In an effort to develop alternative single buffer layer technology for YBa2 Cu3 O7-δ (YBCO) coated conductors, we have investigated LaMnO 3 (LMO) as a potential buffer layer. High-quality LMO films were grown directly on biaxially textured Ni and Ni-W (3%) substrates using rf magnetron sputtering. YBCO films were then grown on LMO buffers using pulsed laser deposition. Detailed X-ray studies have shown that both YBCO and LMO layers were grown with a single epitaxial orientation. Rutherford backscattering spectroscopy (RBS) analyses have indicated the ratio of La to Mn ratio is 1:1. SEM micrographs indicated that 3000-Å-thick LMO films on biaxially textured Ni (100) substrates were dense, continuous and crack-free. A high Jc of over 1 MA/cm2 at 77 K and self-field was obtained on YBCO films grown on LMO-buffered Ni or Ni-W substrates. We have identified LaMnO 3 as a good diffusion barrier layer for Ni and it also provides a good template for growing high current density YBCO films. INTRODUCTION Rolling-Assisted Biaxially Textured Substrates (RABiTS) approach has been emerged as one of the leading techniques for the fabrication of second generation YBa2 Cu3 O7-δ (YBCO) coated conductors. In this approach, the standard three-layer architecture of CeO 2 /YSZ/CeO 2 /Ni is utilized to produce meter lengths of buffered tapes. Here, the CeO 2 seed layer is typical grown by reactive evaporation. Both YSZ barrier and CeO 2 cap layers are grown by rf magnetron sputtering. Recently, we have shown that by using solution Gd2 O3 or La2 Zr2 O7 (LZO) buffers as the seed layers, RABiTS with the architecture of CeO 2 /YSZ/Gd2 O3 or LZO/Ni or Ni-W (3%) can be fabricated in meter lengths. YBCO films grown by ex-situ BaF2 process on 80 cm long, 1 cm wide CeO 2 /YSZ/Gd2 O3 /Ni tapes exhibited end-to-end Jc of 6.25 x 105 A/cm2 at 77 K and selffield [1]. This promises a route for producing long lengths of YBCO coated conductors using both vacuum and non-vacuum buffer layer technologies. In continuation of our effort to develop a single buffer layer technology, we have recently investigated the viability of Lanthanum Strontium Manganate, La0.7Sr0.3MnO3 (LSMO) buffer layer due to its electrical conductivity, good thermal stability, and structural compatibility with YBCO [2]. A Jc of 5 x 105 A/cm2 at 77 K was obtained on YBCO films epitaxially grown LSMO-buffered Ni substrates. The transition temperature, Tc was also suppressed to 87 K. Secondary Ion Mass Spectrometer (SIMS) depth-profile analyses on YBCO/LSMO/Ni indicated the contamination of YBCO layers with Sr from LSMO layers. The diffusion of Ni through LSMO was contained at the LSMO/Ni interface. Hence, LSMO films can be used as a good diffusion barrier layer. Due to the ab
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