Local epitaxy of YBa 2 Cu 3 O x on polycrystalline Ni measured by x-ray microdiffraction
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Polychromatic synchrotron x-ray microdiffraction is used to determine the epitaxy of YBa2Cu3Ox (YBCO) films grown on polycrystalline Y.15Zr.85O1.925/CeO2/Y2O3/ Ni95W5(Ni) rolling-assisted, biaxially textured substrates (RABiTS). A novel analysis technique is introduced in which the orientation of mosaic films is measured by using a Hough transform to recognize arcs in Laue microdiffraction patterns that correspond to low-index zone axes. While the overall epitaxy is cube-on-cube, grain-by-grain analysis reveals a systematic misorientation of YBCO with respect to Ni: the YBCO [001] rotates toward the direction of the surface normal. The crystal mosaic (for rotation about the rolling direction) measured by a single diffraction pattern sampling a 0.5-m2 surface area is 0.7° full width at half-maximum for YBCO grown on Ni grains with a low tilt; for more highly tilted grains, the YBCO patterns can no longer be measured, presumably due to the large mosaic. The YBCO mosaic over the entire area of a Ni grain is ∼2.5° and varies with grain size; the mosaic is smaller for larger grains. I. INTRODUCTION
While high critical current YBa2Cu3Ox (YBCO) superconductors are most easily made by epitaxial growth on single-crystal substrates, practical devices require long conductors made by epitaxial growth on polycrystalline substrates.1–5 This epitaxy has been intensively studied by conventional x-ray diffraction (XRD) techniques, which provide a statistical measure of the epitaxy over a large area but not the orientation of individual grains. Electron backscatter diffraction (EBSD) analysis is a complementary probe, providing a detailed map of the orientation of surface grains, but giving no information about the underlying substrate.6 EBSD and transmission electron microscopy can measure the epitaxy of cross-sectional samples, but only a few grains per sample are observed.6 Multiple EBSD images taken as the surface of a sample is ion-milled from the film down to the substrate has been used to measure grain boundary meander7 and grain alignment.8 This technique requires extensive sample preparation and a smooth surface, and measures relative grain orientation at an angular resolution of ∼0.5°.9 a)
Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www. mrs.org/jmr_policy. c) Present address: Argonne National Laboratory, Argonne, Illinois 60439. DOI: 10.1557/JMR.2007.0091 664
X-ray microdiffraction can provide a complete description of epitaxy with no sample preparation and no limitation on surface roughness, and with high angular resolution. A penetrating 0.7-m beam measures the orientation of both substrate and overlayer. Budai et al.10 used this technique to analyze the growth modes of CeO2 grown on a polycrystalline Ni rolling-assisted biaxially textured substrate (RABiTS). CeO2 grows by island nucleation at low temperatu
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