Pulsed-Laser Deposition of Biaxially Textured YSZ/CeO 2 Films on Electrodeposited Ir/Ni-W Tapes for YBCO Superconductors
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Pulsed-Laser Deposition of Biaxially Textured YSZ/CeO2 Films on Electrodeposited Ir/Ni-W Tapes for YBCO Superconductors
Tapas Chaudhuri, Priscila Spagnol, Raghu Bhattacharya, and Sovannary Phok National Renewable Energy Laboratory, Superconductivity Group, 1617 Cole Blvd., Golden, CO 80401, USA
ABSTRACT Iridium film is a potential candidate as a buffer layer for yttrium barium copper oxide (YBCO) coated conductors. Pulsed laser deposition (PLD) of biaxially textured CeO2/yttrium stabilized zirconium oxide (YSZ) layers on electrodeposited Ir/Ni-W is reported. Biaxial texturing is obtained by deposition of a YSZ seed layer at 800oC in 10-6 Torr vacuum. X-ray diffraction (XRD) studies of θ-2θ and pole figure confirmed in-plane out-of-plane biaxial texturing with ∆ϕ = 6.5o and ∆ω = 8o. Atomic force microscopy (AFM) revealed a surface with roughness of about 3 nm.
INTRODUCTION Buffer layers are the key component in YBCO-coated conductors based on rollingassisted biaxially textured substrates (RABiTS), such as, Ni and nickel alloys [1,2]. These provide chemically inert, continuous and smooth base for the growth of the YBCO film, while transferring the biaxial texture from the substrate to the high-temperature superconductor (HTS) layer. Because YBCO is processed at about 800oC in an oxygen atmosphere of 100 ppm or more, buffer layers also act as barriers to prevent the diffusion of metal to the HTS layer and oxidation of the metal substrate. Different types of buffers layers consisting of two or three films of oxides have been investigated [ 2,3,4]. Recently, Ayug et al. [4] showed that Ir film, deposited by magnetron sputtering, can act as an excellent barrier layer when used as a part of a conductive buffer bilayer structure on NiW tapes. Ir metal, among the platinum group of metals, has excellent resistance to oxidation and corrosion and low oxygen diffusivity. Further, even IrO2 is chemically inert and exhibits metallic conduction. In our laboratory, we developed [5] electrodeposited Ir coating as a buffer layer on Ni-W substrates. This paper reports on the deposition of biaxially textured CeO2/YSZ layers by pulsed-laser deposition (PLD) on Ni-W tapes electroplated with Ir and their characterization by X-ray diffraction (XRD) and atomic force microscopy (AFM). EXPERIMENTAL The Ir films were deposited in a vertical electrochemical cell in which the electrodes (both working and counter) were suspended vertically from the top. The bath contained only 0.5 g Ir salt dissolved in deionized water. The electrodeposition (ED) experiments were performed at 65oC without stirring the solution. The ED precursors were prepared
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at about 1.2 V from 2 to 15 min on Ni-W (3 at.%), where the Pt counter and Pt pseudoreference were shorted together. The PLD system consisted of a standard PLD chamber (Neocera) and an excimer KrF laser (Lambda Physik, Compex 201, λ=248 nm) operated at 260 mJ and 10 Hz. The laser beam is focused onto a 3 x 1cm2 spot on a target at a 45o angle, with a fluence of 2–3 J/cm2. YSZ (3 mole% Y2O
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