Synthesis and Interface Structure of Sol Gel YBa2Cu 3 O x Thin Films for Conductor Development
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Synthesis and Interface Structure of Sol Gel YBa2Cu3Ox Thin Films for Conductor Development Donglu Shi, Yongli Xu, S. X. Wang1, L. M. Wang1, and Shaun M. McClellan Department of Materials Science and Engineering, University of Cincinnati Cincinnati, OH 45221-0012 1 Dept. of Nuclear Engineering and Radiological Science, University of Michigan Ann Arbor, MI 48109 ABSTRACT In our previous work we have obtained YBCO thick films on silver alloy substrate via the peritectic solidification. To further develop grain-textured YBCO thin films for conductor development, in this study, we have used a sol gel approach to deposit YBCO thin films on two different substrates, namely, yttrium-stabilized zirconia (YSZ) and a silver alloy containing 10 % of palladium (Ag –10%Pd). We have found that the sol gel film on YSZ exhibits an epitaxial growth. This is confirmed by both x-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). XRD data also indicate that the YBCO film on Ag-10%Pd has a c-axis grain orientation. The details are reported on sol gel synthesis and XRD and HRTEM characterization of the YBCO thin films. INTRODUCTION To improve the transport properties of high temperature superconductors, extensive experimental investigations have been carried out in developing highly textured thin films on a variety of substrates (1-8). Among all synthesis techniques, the fabrication of YBCO films by eptaxial deposition on rolling assisted biaxially textured substrates (RABiTS) has been most successful in the conductor development for large-scale applications (9-11). The RABiTS technique uses well-established industrially scaleable thermochamical processes to impart a high degree of grain texture to a base metal. The buffer layers are then deposited to yield chemically and structurally compatible surfaces. Eptaxial YBCO films are grown on such a surface resulting in a critical current density on the order of 106 A/cm2 (9,10). This novel approach has shown a promise for developing long conductors for industrial applications. However, in some large-scale applications of superconductivity, the conductors are required not only to carry high critical current density at respectable magnetic fields but also to possess high ductility, mechanical strength, and stability. The so-called stabilizer is achieved through cladding the superconducting material with metallic conductors. In this way, in case of quenching, the large amount of electrical current can be carried by the stablizer. In RABiTS thin films, several buffer layers must be deposited prior to YBCO formation. The buffer layers are insulators which cannot serve as a stablizor that is essential for conductor development. It is, therefore, important to seek for ways of depositing YBCO films directly on a metallic substrate without buffer layers. In our previous works (12-14), we have shown the possibilities of obtaining c-axis grain II6.4.1
orientated YBCO thick films on the silver alloy substrate via a high-temperature melt processing. In this study, we re
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