Texture Formation and Superconducting Properties of YBa 2 Cu 3 O x Thin Films Prepared by Solution Process on LaAlO 3 Si
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Texture Formation and Superconducting Properties of YBa2Cu3Ox Thin Films Prepared by Solution Process on LaAlO3 Single Crystals Y.-A Jee, B. Ma, M. Li, B. L. Fisher, and U. Balachandran Energy Technology Division, Argonne National Laboratory, Argonne, IL 60439, U.S.A. ABSTRACT YBa2Cu3Ox (YBCO) thin films were fabricated by the trifluoroacetate (TFA) process on LaAlO3 (LAO) single crystal in an argon atmosphere. We focused on lowering the heat treatment temperature by decreasing the oxygen partial pressure to adopt the TFA process to metallic substrates. YBCO phase formation was checked by measuring Tc with the inductive method. In-plane and out-of-plane film textures were evaluated by phi-scan and omega scan, respectively. Raman spectroscopy was used to estimate grain connectivity, in-plane texture, and second-phase formation of the films. Although Raman spectroscopy revealed some evidence of cation disorder, the film prepared at 750oC shows a sharp superconducting transition at 91 K and critical current density of 1.3 MA/cm2 at 77 K. Optimal heat treatment temperature was 750oC in the argon atmosphere, which is consistent with the thermodynamic estimate that heat treatment temperature decreases as oxygen partial pressure decreases. INTRODUCTION For fabrication of YBCO-coated conductors on metal substrates, various processing methods were investigated to achieve high Jc values. Vacuum processes [1-3] generally produce high-Jc films, and the related buffer layers are also prepared by vacuum processes such as ion beam assisted deposition. However, in terms of long-length applications of coated conductors, complicated vacuum equipment and a high-cost process may not be appropriate. On the contrary, nonvacuum ex-situ processes such as metal organic decomposition (MOD) and the solgel process seem to be more promising. The solution techniques are now being studied by several investigators [4-11], and some of their results are comparable to those obtained by vacuum processes. MOD using trifluoroacetate (TFA) produces one of the highest Jc values of all the solution techniques, but its application to metal substrates is still not consistently successful due to the lack of full understanding of processing condition. In this study, we report our work on systematically optimizing the parameters of the TFA process. Toward application to metal substrates, we have concentrated especially on lowering the heat treatment temperature. EXPERIMENTAL DETAILS Metal acetates of Y, Ba and Cu in the molar ratio of 1:2:3 were dissolved in trifluoroacetic acid and refluxed for 4 h. This solution was then dried in air to evaporate the solvent and to obtain a blue solid residue. The solid residue is easily soluble in methanol, and this methanol-based solution was used throughout our experiment. The solution was coated on LAO single crystals with either a dip-coating or a spin-coating method. The precursor film was converted to an epitaxial YBCO film through two separate heat treatments. During the first step (Fig. 1a),
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