Development of Electrodeposited Iridium as a Buffer Layer for YBCO Superconductors
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Development of Electrodeposited Iridium as a Buffer Layer for YBCO Superconductors Priscila Spagnol, Tapas Chaudhuri, Raghu Bhattacharya, and Sovannary Phok National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401, USA ABSTRACT Electrodeposition (ED) is a potentially low-cost, non-vacuum, high-rate deposition process that can easily deposit uniform film on large non-planar substrates. In this paper, we report on successful biaxial textured electrodeposition of Ir on Ni-W substrates. Ir metal is well known for its excellent oxidation and corrosion resistance among platinumgroup elements; also, the lattice mismatch of cubic Ir is very close to that of CeO2 and Ni. The films were deposited in a vertical cell in which the electrodes (both working and counter) were suspended vertically from the top of the cell. The ED experiments were performed at 65oC without stirring the solution. The ED precursors were prepared at about -1.2 V from 2 to 15 minutes on Ni-W, where the Pt counter and Pt pseudoreference electrodes were shorted together. To qualify the electrodeposited Ir buffer layer, a CeO2/YSZ/CeO2 and YSZ/CeO2 buffer structure was later deposited on ED Ircoated Ni-W substrates by pulsed-laser deposition. The ED Ir/metal substrates were first heated at 800oC in 0.5 mTorr of forming gas, and then a CeO2 seed layer was deposited in 180 mTorr of forming gas. Subsequently, YSZ and CeO2 layers were deposited sequentially in 0.1 mTorr of oxygen.
INTRODUCTION The superconductor research community is focusing on improving the quality of the second-generation high-temperature superconductor, YBa2Cu3O7-δ, due to its high critical current density and intrinsically high irreversibility field. One configuration for YBCO on a rolling-assisted biaxially textured (RABiTS) [1,2] substrate consists of a seed layer of CeO2, a barrier layer of YSZ, and a cap layer of CeO2 finishing the structure with the YBCO deposition. Different configurations, materials, and deposition techniques have been evaluated to simplify or improve the current buffer-layer structure. The idea is to develop a buffer layer that will stop the interdiffusion of Ni and W from the substrate into the superconductor layer and will also stabilize the superconductor during an over-current situation. The buffer layers play an important role in the finished YBCO superconductor tape. They are responsible for providing a continuous, smooth, chemically inert surface, mechanical stability, and good adhesion for the growth of YBCO film, while transferring the biaxial texture from the substrate to the superconductor layer. The buffer layer can be deposited by different techniques, such as electron-beam evaporation, sputtering, pulsed-laser deposition (PLD), metalorganic chemical vapor deposition, chemical solution deposition, and electrodeposition. Our group has demonstrated the successful deposition of buffer layers by non-vacuum electrodeposition [3–5]. Advantages of electrodeposition include: (a) potential low cost; (b) a significant
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