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Phase Diagram Studies in the SrO-CuO-TiO2 System; Applications to YBCO Coated Conductors A. Ayala, T.G. Holesinger, E.J. Peterson, and M. Archuleta Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545 U.S.A. ABSTRACT SrTiO3 (STO) is a potential buffer layer material for use in YBa2Cu3Oy (YBCO) coated conductors based on the IBAD MgO process. However, the interactions with YBCO are not yet fully understood and little information exists in the way of phase diagrams. With this in mind, the tie-line between STO and SrCuO2 in the pseudo-ternary system SrO-CuO-TiO2 was investigated. Phase assemblages and compositions were determined by x-ray diffraction and electron microscopy in the temperature range of 1000oC to 1100oC in oxygen partial pressures of 1%, 10%, and 100%. Preliminary results showed that an appreciable amount of copper substitutes into the STO crystal structure. Conversely, Ti substitution into the SrCuO2 phase was not detected. INTRODUCTION YBa2Cu3Oy (YBCO) coated conductors typically consist of three parts: a textured template, an intervening buffer layer or layers, and the superconducting film[1-3]. One method of developing a textured template is to deposit a textured film on a polycrystalline substrate using ion-beam-assist-deposition (IBAD) [4]. Yttria-stablized zirconia (YSZ) is the most common film deposited by IBAD for the textured template. However, IBAD MgO has recently received a significant amount of attention in that the latter process is 100 times faster than IBAD YSZ in forming the textured film [5,6]. One reason that IBAD MgO is not more widespread is that some difficulty has been encountered in developing a suitable intervening buffer layer on to which YBCO can reliably be deposited. SrTiO3 (STO) is a candidate material for the intervening buffer layer. High-quality YBCO films are routinely grown on single-crystal STO substrates. However, little is known about the reactivity between YBCO and STO. While the latter problem rarely appears during deposition onto single crystal substrates, the deposition of YBCO onto a textured, polycrystalline film of STO may change this behavior. With this in mind, the investigation of the SrO-CuOTiO2 psuedo-ternary phase diagram was started. There is no information in the literature regarding this particular phase diagram. In the present work, an emphasis was placed on the tieline between STO and SrCuO2. EXPERIMENTAL PROCEDURE The starting materials used for powder preparations were 99.999% pure SrCO3, CuO, and TiO2. Three precursor powders of SrCuxTiyOz and two samples for use as standards (SrCuO2, STO) were prepared. The precursor powder compositions are SrCu0.1Ti0.9Ox(sample 1), SrCu0.5Ti0.5Ox (sample 2), and SrCu0.2Ti0.9Ox (sample 3). The two standards and sample 1 were prepared by mixing calculated proportions of the starting materials in isopropanol in a motorized E8.24.1

Figure 1. SEM backscattered electron micrographs of the (a) STO and (b) SrCuO2 standards used in the compositional quanitification process i