Microstructure of Epitaxial Y123 Films on CeO2-Buffered YSZ Prepared by Fluorine-Free MOD

Epitaxial YBa₂Cu₃O₇ (Y123) films have been prepared by fluorine-free metalorganic deposition (MOD) using a metal acetylacetonate-based coating solution on cerium oxide (CeO₂: 40 nm)-buffered yttria-stabilized zirconia (CbYSZ) substrates. The 210-nm-thick Y123 film demonstrated a high critical current density (J_c), the average J_c being 4.5 MA/cm² at 77.3 K using an inductive method. However, with increasing thickness the Jc values decreased; the average J_c was 3.4 and 2.2 MA/cm² for 400-nm- and 550-nm-thick films, respectively. In low-magnification cross sectional transmission electron microscopy (XTEM) images for the films, the stripe-like contrast due to the c-axis orientation of Y123 was clearly seen from the interface with CeO₂ to the surface. The whole c-axis-oriented Y123 layers were very dense even in the 550-nm-thick film. Full width at half maximum (FWHM) of Deltaomega for the 308/038 reflections in XRD omega - 2thetas scanning decreased with increasing film thickness. High resolution XTEM images of the 550-nm-thick film showed wavy c-planes of Y123 due to the short stacking faults near the interface with CeO₂ buffer and near the surface whereas the c-planes were very flat but contained long stacking faults in the middle part of the film. It is suggested that the absence of wavy stacking faults, which probably work as pinning centers, decreased J_c in the thicker films. Further decrease in J_c in the 550-nm-thick film is presumably caused by the roughness in the outer layer near the surface.