Research and Development of Biaxially Textured IBAD-GZO Templates for Coated Superconductors
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Research and
Development of Biaxially Textured IBAD-GZO Templates for Coated Superconductors
Yasuhiro Iijima, Kazuomi Kakimoto, Yutaka Yamada, Teruo Izumi, Takashi Saitoh, and Yuh Shiohara Abstract Ion-beam-assisted deposition (IBAD) has been used to prepare biaxially textured templates necessary to realizing high superconducting performance in coated conductors. The IBAD method is characterized by the direct deposition of sharply aligned templates on nontextured metal substrates using fluorite-like oxide films (yttrium-stabilized zirconia, Gd2Zr2O7, etc.). Recent progress in vacuum technology for IBAD has made it possible to reproducibly fabricate long lengths (100 m) of IBAD-GZO templates. Continuous deposition of YBCO films on these templates has been achieved by pulsed laser deposition (PLD). Furthermore, a new approach to improving the texture of IBAD templates was found by using CeO2 films grown by PLD. Trifluoroacetate-based metalorganic deposition has also been used instead of PLD to produce superconducting layers on IBAD buffered tapes, aiming at a low-cost process. This article reviews progress in the research and development of biaxially textured templates produced using IBAD and their subsequent use in fabricating superconducting tapes and wires by means of several processes. Keywords: Gd2Zr2O7, GZO, high-temperature superconducting wires, ion-beam-assisted deposition, pulsed laser deposition, trifluoroacetate-based metalorganic deposition, YBCO-coated conductors.
substrate materials to be considered, based on such properties as mechanical strength, magnetic characterization, or cost rather than whether they can serve as a template for conductors; (2) it produces templates with an excellent biaxial texture, a smooth surface, and a small grain size (5–10 nm), which completely hides the large grain boundaries of the metal substrate below; and (3) it causes no thermal damage of the substrate surface during deposition of the template films. Recent advancements in vacuum technology for both IBAD and pulsed laser deposition (PLD) have resulted in the fabrication of long lengths (100 m) of coated conducting tape with a large critical current density (Jc); the value of critical current (Ic) multiplied by length (L) reached nearly 4000 A m.5,6 This article describes recent developments in IBAD template materials to substitute for yttrium-stabilized zirconia (YSZ),7 long-length processing using IBAD and PLD (up to 100 m),6 drastic texture improvement of template films by means of CeO2 films grown by PLD,8 the dependence of Jc on thickness and full width at half maximum for in-plane texture () in YBCO films grown by PLD;9 and the potential for low-cost processing using trifluoroacetate-based metalorganic deposition (TFA-MOD) for YBCO films on IBAD templates.10
Development of IBAD Template Materials The IBAD method is a type of vaporphase deposition using concurrent ionbeam bombardment during film growth.11 Table I shows the properties of in-plane textured template films prepared by IBAD. Off-normal ion-beam
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