Growth of c-axis-oriented films of YbBa2Cu3O7-δ on single and polycrystalline MgO substrates by oxidation of a liquid alloy precursor

Textured superconducting films of YbBa2Cu3O7-δ supported on both single and polycrystalline MgO substrates were prepared by oxidation of a liquid precursor alloy. The substrates were coated by dipping them into the molten alloy (YbBa2Cu3, melting point ∝870degC). After withdrawal from the melt, the adhering metal was oxidized to the corresponding oxide phase, i.e., Yb-Ba2Cu3O7-δ, which exhibited a superconducting transition at ∝80 K following annealing in pure O2 at 500degC. With MgO(100) substrates, evidence was seen for the epitaxial growth of YbBa2Cu3O7-δ crystals having their c-axis parallel to the [100] direction of the substrate. For polycrystalline MgO, X-ray diffraction and microstructural examination showed that the high-Tc crystallites in the films were also oriented with their c-axis perpendicular to the substrate surface, but the directions of the a and b axes were disordered rather than epitaxial. The superconducting properties of as-prepared films are discussed together with the effects of key processing parameters on composition and microstructure. (orig.)