Solution-processed lanthanum zirconium oxide as a barrier layer for high I c -coated conductors
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Thomas Kodenkandath, Xiaoping Li, and Martin W. Rupich American Superconductor Corporation, Westborough, Massachusetts 01581 (Received 13 October 2005; accepted 22 December 2005)
High-quality lanthanum zirconium oxide (La2Zr2O7 or LZO) films have been deposited and processed on Ni–W substrates using a sol-gel processing approach. It has been demonstrated that crack-free coatings with thicknesses up to 100 nm can be processed in a single step, while thicker coatings (200–225 nm) were processed using a multiple coating and annealing process. Using simulated metalorganic deposition (MOD)-YBa2Cu3O7−␦ (YBCO) processing conditions, the barrier properties of the sol-gel LZO coating with a thickness of 120 nm were found to be comparable to that of the standard 3-layer buffer stack deposited using physical vapor deposition. Secondary ion mass spectroscopy depth profile analysis of LZO films annealed in oxygen-18 shows that LZO effectively stops the diffusion of Ni within the first 80–100 nm. Using MOD processes, a CeO2 cap layer and superconducting YBCO layer were deposited on sol-gel LZO/Ni–W. For the first time, using such an all-solution conductor architecture, a critical current (Ic) of 140 A/cm with a corresponding critical current density (Jc) of 1.75 MA/cm2 has been demonstrated. Using a very thin Y2O3 seed layer (∼10 nm) deposited by electron beam evaporation; improved texture quality in the LZO layers has been demonstrated. The performance of the LZO deposited on these samples was evaluated using a sputtered CeO2 cap layer and MOD YBCO layer. Critical currents of up to 255 A/cm (3.2 MA/cm2) with 0.8-m-thick YBCO films have been demonstrated, comparable to the performance of films grown using physical vapor deposited yttria stabilized zirconia as a barrier layer. Similar experiments using an MOD-CeO2 cap layer and MOD-YBCO layer yielded critical currents of 200 A/cm (2.5 MA/cm2) with 0.8-m-thick YBCO films.
I. INTRODUCTION
One of the main focus areas of research in hightemperature superconductivity (HTS) in recent years has been on the development of second-generation wires also known as coated-conductors.1–6 One of the leading textured-template approaches for the fabrication of coated-conductors is the rolling assisted biaxially textured substrates (RABiTS) approach.3,4 In this approach, cube-textured nickel or Ni alloy substrates, obtained by cold rolling and recrystallization, function as a template for the epitaxial deposition of buffer layers and the YBa2Cu3O7–␦ (YBCO) superconductor. The buffer layers provide a structural template for the HTS layer and
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0112 910
J. Mater. Res., Vol. 21, No. 4, Apr 2006 http://journals.cambridge.org Downloaded: 07 Feb 2015
also act as a chemical barrier between the metal substrate and the HTS coating. Using such architecture, sufficient biaxial texturing of the HTS layer has been obtained to avoid problems associated with weak-linked, high-angle grain boundaries.7 To date,
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