Chemical solution deposition of lanthanum zirconate barrier layers applied to low-cost coated-conductor fabrication
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X. Li, U. Schoop, T. Kodenkandath, and M.W. Rupich American Superconductors Inc., Westborough, Massachusetts (Received 17 November 2003; accepted 25 March 2004)
Epitaxial lanthanum zirconate (LZO) buffer layers have been grown by sol-gel processing on Ni–W substrates. We report on the application of these oxide films as seed and barrier layers in coated conductor fabrication as potentially simpler, lower cost coated-conductor architecture. The LZO films, about 80–100-nm thick, were found to have dense, crack-free surfaces with high surface crystallinity. Using 0.2-m YBCO deposited by pulsed laser deposition, a critical current density of 2 MA/cm2 has been demonstrated on the LZO films (YBCO/LZO/Ni–W). Using 0.8-m YBCO deposited using metal organic decomposition, a critical current density of 1.7 MA/cm2 and a critical current of 135 A/cm have been demonstrated on the LZO barrier layer with a sputtered CeO2 cap layer (YBCO/CeO2/LZO/Ni–W). These results offer promise to replace several of the vacuum-deposited layers in the typical coated conductor architecture (YBCO/CeO2/YSZ/Y2O3/Ni/Ni-W).
I. INTRODUCTION
Fabrication of high-temperature superconductors (HTS) in wire form based on epitaxial deposition on biaxially textured substrates has been a major worldwide research thrust for the past few years. Currently, three technologies are being explored to fabricate conductors by epitaxial deposition of YBCO and other superconducting materials on biaxially textured substrates—ionbeam-assisted deposition,1–4 inclined substrate deposition,5–7 and rolling-assisted biaxially textured substrates (RABiTS).8–12 In the RABiTS approach, biaxial texture is first produced in the metal substrate using thermomechanical processing, and various epitaxial layers are deposited on the metal substrate using industrially scalable processing techniques. Currently, a common RABiTS architecture employs a Ni–3 at.% W (Ni–W) alloy substrate with a nickel overlayer, followed by a buffer layer sequence of Y2O3/YSZ/ CeO2.13 The superconductor is then deposited on the CeO2 cap layer. A variety of deposition techniques are used for the deposition of the various layers. The Ni overlayer is deposited using dc-sputtering,13 the Y2O3
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Address correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0281 J. Mater. Res., Vol. 19, No. 7, Jul 2004
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seed layer is deposited using electron beam evaporation,14 and the YSZ barrier layer and the CeO2 cap layer are deposited using rf-sputtering.15 Due to the use of several layers deposited using a variety of vacuum deposition techniques, the scale-up of this architecture becomes complex and expensive. We have previously reported our results on the deposition of lanthanum zirconium oxide (LZO) seed layers directly on Ni–W substrates with consistent and reproducible properties and a critical current density (Jc) up to 2 MA/cm2 using a scalable nonvacuum solution-based deposition technique.16 We found that LZO seed layers can be con
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