High pinning performance of YBa₂Cu₃O7-x films added with Y₂O₃ nanoparticulate defects

We report the epitaxial growth and superconducting properties of Y₂O₃-added YBa₂Cu₃Ox (YBCO) films grown on SrTiO₃-buffered MgO substrates by pulsed-laser deposition using surface-modified YBCO targets. Areas of Y₂O₃ sectors on the YBCO target were increased to 5.44% and 9.22% of the total YBCO pellet in order to find a correlation between the Y₂O₃ content, morphology, and the pinning properties of YBCO+Y₂O₃ mixed films. The maximum global pinning forces, FP, at 77 K were 14.3 GN m^-3 and 1.15 GN m^-3 for the Y₂O₃ 5.44A% and 9.22A%, respectively. The 5.44A% Y₂O₃-added sample presents a very high value of pinning force at 77 K, approaching the value obtained in YBCO films with added BaZrO₃ nanorods, but with less depression in the superconducting critical temperature, Tc. In accordance with scanning transmission electron microscopy (STEM) observations, both films present nanoparticulate Y₂O₃ dispersed in a YBCO matrix where Y₂Ba4Cu8O16 (Y248) intergrowths were also observed. Consistent with the strong pinning theory, the size and distribution of randomly dispersed Y₂O₃ particles are optimal for the flux pinning of a 5.44A% Y₂O₃-YBCO film, while in the case of a 9.22A% film, the YBCO matrix is degraded by jam-packed Y248 intergrowth, which leads to a comparatively poor pinning performance. We further used the single-vortex dynamics model to account for vortex pinning in the samples. The 5.44A% Y₂O₃-YBCO film result shows good agreement with the model fit up to 4 T of the applied magnetic field.