Preparation of High-Jc YBa2Cu3O7-y Films on CeO2-Buffered Yttria-Stabilized Zirconia Substrates by Fluorine-Free Metalorganic Deposition

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Epitaxial YBa2Cu3O7-y (YBCO) films have successfully been prepared by fluorine-free metalorganic deposition on yttria-stabilized zirconia (YSZ) substrates with an evaporated CeO2 buffer layer. The YBCO films, prepared using a metal acetylacetonate-based coating solution, were highly (001)-oriented by X-ray diffraction θ–2θ scanning and φ scanning. The 0.21-µm-thick YBCO film demonstrated a high superconducting transition temperature, Tc=90.1 K, and high critical current densities with an average in excess of 4 MA/cm2 at 77 K using an inductive method. Transport critical current (Ic) was also measured by a standard four-terminal technique; the Ic value reached 185 A in a 2.5-cm-wide current path formed on a 5-cm-diameter film. These excellent properties are attributed to the small in-plane fluctuation due to high epitaxy of the YBCO films, which resulted from good matching of the crystal structure, lattice parameter and thermal expansion coefficient among the YBCO film, CeO2 buffer layer and YSZ substrate, as well as from the smooth and uniform surface morphology, i.e., average roughness = 0.34 nm, of the CeO2 buffer layer. The present deposition conditions, i.e., 700°C and p(O2)=4×10-2 Pa, activated by radio frequency plasma at 20 W, are valid for the growth of such CeO2(100) buffer layers on YSZ substrates.