High pinning performance of YBa2Cu3O7−xfilms added with Y2O3nanoparticulate defects

We report the epitaxial growth and superconducting properties of Y 2 O 3 -added YBa 2 Cu 3 Ox (YBCO) films grown on SrTiO 3 -buffered MgO substrates by pulsed-laser deposition using surface-modified YBCO targets. Areas of Y 2 O 3 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 Y 2 O 3 content, morphology, and the pinning properties of YBCO + Y 2 O 3 mixed films. The maximum global pinning forces, F P , at 77 K were 14.3 GN m −3 and 1.15 GN m −3 for the Y 2 O 3 5.44A% and 9.22A%, respectively. The 5.44A% Y 2 O 3 -added sample presents a very high value of pinning force at 77 K, approaching the value obtained in YBCO films with added BaZrO 3 nanorods, but with less depression in the superconducting critical temperature, T c . In accordance with scanning transmission electron microscopy (STEM) observations, both films present nanoparticulate Y 2 O 3 dispersed in a YBCO matrix where Y 2 Ba 4 Cu 8 O 16 (Y248) intergrowths were also observed. Consistent with the strong pinning theory, the size and distribution of randomly dispersed Y 2 O 3 particles are optimal for the flux pinning of a 5.44A% Y 2 O 3 -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% Y 2 O 3 -YBCO film result shows good agreement with the model fit up to 4 T of the applied magnetic field.