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Engineered Microstructures and Transport Properties in YBCO Coated Conductors T.G. Holesinger, B.J. Gibbons, J.Y. Coulter, S.R. Foltyn, J.R. Groves, and P.N. Arendt Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545 U.S.A. ABSTRACT Each process used to deposit or make the bi-axially textured template, buffer layer(s), and the superconductor in a coated conductor creates interfaces along which defects or interfacial reactions may result. These defects can be additive and propagate through the entire film structure to affect the growth and properties of the superconducting film. Defects within the films and their corresponding transport properties have been correlated with the differences in the thickness of the underlying buffer layer material. This knowledge can be used to control and engineer the structure of the coated conductor to maximize critical current densities. INTRODUCTION The production of the so-called second-generation “coated conductors” requires a biaxially-textured template for the subsequent oriented growth of additional oxide buffer layers and YBa2Cu3Oy (YBCO) [1-3]. Ion-beam-assisted deposition (IBAD) is one approach that is used for preparing a biaxially-aligned buffer layer on polycrystalline nickel-alloy substrates. In general, YBCO films may be deposited directly onto the IBAD YSZ or MgO templates. However, additional buffer layers have been found to be beneficial in optimizing the transport properties and controlling defects in the Y-123 films [4-9]. Because the coated conductor process is a layering process, several interfaces are formed along which defects or interfacial reactions may result. These defects can be additive and propagate through the entire film structure to affect the growth and properties of the YBCO film. Structural defects, chemical defects, or a combination of both are often formed along the various interfaces [6,7,10-12]. Their origins include substrate roughness, lattice mismatch, porosity, contamination, adhesion problems, and interfacial reactions. One area of specific concern is the underlying buffer layer to the YBCO film. CeO2 is often used successfully as this buffer layer as it is a stable oxide with a good lattice match to YBCO [3,4,13]. However, even ceria reacts with YBCO and affects the superconductor’s properties [6]. Since it appears that nearly all materials that have been used as buffer layers react with Y-123 at typical processing temperatures, it is especially important to understand what general aspects of the interfacial reactions between a given material and Y-123 have on the superconducting transport properties. In this paper, various aspects of defect generation in YBCO coated conductors are discussed. Particular attention was paid to the role of the underlying buffer layer to the YBCO and how its thickness can influence the stability of the interface and the properties of the superconducting film. EXPERIMENTAL IBAD was used to produce the biaxially-textured YSZ films on Inconel 625 or Hastelloy substrat