Chemical solution deposition of lanthanum zirconate buffer layers on biaxially textured Ni-1.7% Fe-3% W alloy substrates
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W. Kang, P.M. Martin, A. Goyal, and D.M. Kroeger Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6116
D.K. Christen Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6061 (Received 15 August 2001; accepted 1 April 2002)
Sol-gel processing of La2Zr2O7 (LZO) buffer layers on biaxially textured Ni–1.7% Fe–3% W alloy substrates using a continuous reel-to-reel dip-coating unit has been studied. The epitaxial LZO films obtained have a strong cube texture and uniform microstructure. The effects of increasing the annealing speed on the texture, microstructure, and carbon content retained in the film were studied. On top of the LZO films, epitaxial layers of yttria-stabilized zirconia and Ceria (CeO2) were deposited using rf sputtering, and YBa2Cu3Ox (YBCO) films were then deposited using pulsed laser deposition. Critical current densities (Jc) of 1.9 MA/cm2 at 77 K and self-field and 0.34 MA/cm2 at 77 K and 0.5 T have been obtained on these films. These values are comparable to those obtained on YBCO films deposited on all-vacuum deposited buffer layers and the highest ever obtained using solution seed layers.
I. INTRODUCTION
Current trends in research and development in hightemperature superconductivity (HTS) are geared toward fabrication of YBa2Cu3Ox (YBCO)-coated conductors. A coated conductor is defined as the superconductor deposited on a long-length textured substrate. The different stages involved in coated conductor fabrication are the following: (a) development of long lengths of flexible metal substrate; (b) deposition of textured buffer layers which will act as a crystallographic template for further growth of the HTS film while preventing the diffusion of the metal from the substrate to the HTS film; (c) deposition of the HTS film. To fabricate coated conductors in long lengths, it is imperative that the processing techniques used in each stage must be scalable. The chemical solution deposition technique has been proven to be a viable low-cost nonvacuum process for coating long lengths.1–6 Rolling assisted biaxially textured substrates are ideal templates for the solution process.7–9 Solution precursors can be used for processing both buffer layers and superconductor films.10–12 Typically, in this process, the substrates are coated with a metalorganic precursor solution at room temperature followed by a hightemperature anneal to obtain highly crystalline phases. The main advantage of using solution precursors is the ease with which precursor stoichiometry can be controlled.
Buffer layer architectures currently in use consist of three components, a seed layer, a barrier layer, and a cap layer. Most promising results have been obtained using yttria-stabilized zirconia (YSZ) as the barrier layer and CeO2 as the cap layer. However, due to the difficulties involved in growing epitaxial YSZ films directly on Ni substrates, a seed layer is required to fabricate textured substrates for useful coated conductors. Early attempts to grow epitaxial buf
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