Rare-earth mixed oxide thin films as 100% lattice match buffer layers for YBa₂Cu₃O_7-x coated conductors

Buffer layers with 100% lattice match with YBa₂Cu₃O_{7 - δ} (YBCO) were prepared from mixed rare-earth-oxides applying a simple sol-gel process and dip-coating method. Structural analysis of the sol-gel derived powder by X-ray diffraction revealed that the mixing parameter, which eliminates the lattice mismatch with YBCO, is x = 0.2382, 0.1852, 0.1252, 0.0906, 0.0793 and 0.0395 in (Eu_{1 - x}Ho_x)₂O₃, (Eu_{1 - x}Er_x)₂O₃, (Eu_{1 - x}Yb_x)₂O_3, (Gd_{1 - x}Ho_x)₂O₃, (Gd_{1 - x}Y_x)₂O₃ and (Gd_{1 - x}Yb_x)₂O₃, respectively. Microstructural investigations were carried out for Gd_1.819Ho_0.181O₃ films epitaxially grown on cube-textured Ni (100) substrates by sol-gel dip-coating process. X-ray diffraction of the buffer showed strong out-of-plane orientation on Ni tape. The (Gd_{1 - x}Ho_x)₂O₃ (222) pole figure indicated a single cube-on-cube textured structure. The omega and phi scans revealed good out-of-plane and in-plane alignments. The full-width at half-maximum values of omega and phi scan of (Gd_{1 - x}Ho_x)₂O₃ films was observed at 4.21° and 6.81°, respectively. Micrographs of the film obtained by using environmental scanning electron microscope and atomic force microscope revealed pinhole-free, crack-free, smooth and dense microstructures.