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Epitaxial YXBa2Cu3O7-δ (YXBCO) thin films were deposited by pulsed laser deposition on both single crystal SrTiO3 (100) and buffered polycrystalline metal substrates, where X=0.9, 1.0, 1.1, 1.2, and 1.3. The self-field critical current density (Jc) of YXBCO exhibits the best performance at X=1.1 for the samples on both single crystal substrates and metal substrates. Epitaxial Y2O3 nanoparticles were observed in Y-rich samples (X>1.0) by X-ray diffraction and cross-sectional transmission electron microscopy. The field-dependence and angular-dependence measurements show that Y2O3 nanoparticles improve the in-field Jc performance, especially in the low field regime, without reducing self-field Jc of YBCO films. [ABSTRACT FROM AUTHOR]

Microstructural evolution with the change in thickness of superconducting YBa2Cu3O7-x films on single-crystal SrTiO3 substrates deposited by pulsed laser deposition was evaluated using different structural characterization tools. A noticeable degradation of crystallinity with the increased film thickness was detected. Nevertheless, a comprehensive relationship between the microstructure and the zero-field current-density can not be established solely based on the degradation of crystallinity. [ABSTRACT FROM AUTHOR]

We conducted a comparative study of microstructural properties for YBa2Cu3O7 (YBCO) films on single-crystal MgO and polycrystalline Ni-based metal substrates with ion-beam-assisted deposited (IBAD) MgO as a template. The film grown on the metal substrate shows more crystalline imperfections with density of screw dislocations four times higher than that of the film on single-crystal MgO, as revealed by high-resolution x-ray diffraction (HRXRD). These high-density screw dislocation cores connect well and form bigger clustered grains as detected by scanning tunneling microscopy. Transmission electron microscopy studies confirm that the structural quality of YBCO on the Ni-based alloy is comparable to that on single-crystal MgO. All these factors contribute to our routine fabrication of high-quality YBCO films on metal substrates with critical current densities in self-field as high as those for the films grown on single-crystal MgO substrates. Superconducting properties in fields are also discussed. [ABSTRACT FROM AUTHOR]

YBa2Cu3Oy (YBCO) films produced by the ex situ conversion of BaF2-based precursors deposited by physical vapor deposition on ion-beam assisted deposited (IBAD) yttrium-stabilized zirconia (YSZ) and rolling-assisted biaxially textured substrates (RABiTS) templates are characterized by a bi-axially aligned, laminar grain structure that results from the anisotropic growth characteristics of the YBCO phase and its precipitation from a transient liquid phase during the conversion process. A bimodal microstructure characterizes these films and is defined by large, well-formed YBCO grains with Y2O3 precipitates in the bottom region of the film and small YBCO grains with a high density of stacking faults in the upper half. Ba2Cu3Oy or Ba-O-F/CuO second phase layers were often found between large YBCO grains in the bottom half of the films. YBCO grain sizes exceeded 50 µm within the plane of the film in some cases. Conversely, discrete secondary phases of Y2Cu2O5, Y2O3, and Ba2Cu3Oy/Ba-O-F could be found among the much smaller YBCO grains in the top portion of the bimodal structure. The dividing line of the bimodal structure was generally at one half of the film thickness, although exceptions to this trend were found. The highest critical current densities (Jc) and best film alignments for a given film thickness were found in samples where the layers of Ba2Cu3Oy or Ba-O-F were minimized or eliminated from the films. Samples quenched after partial conversion show the segregation of CuO to the top region of the film and the lateral growth of large YBCO grains from a precursor mix of Y2Cu2O5 and Ba-O-F. The data demonstrate that transient liquid phases are part of the conversion process of... [ABSTRACT FROM AUTHOR]