Incorporation of double artificial pinning centers in YBa₂Cu₃O_7-δ films

YBa₂Cu₃O_7-x + BaZrO₃ + Y₂O₃ (YBCO + BaZrO₃ + Y₂O₃) mixed films were prepared on SrTiO₃/MgO substrates by pulsed-laser deposition from an YBCO + BaZrO₃ target with a thin Y₂O₃ sector stuck on the top. The pinning properties for the double-doped YBCO + BaZrO₃ + Y₂O₃ thin film were enhanced in comparison with a pure YBCO sample prepared in the same experimental conditions. The maximum global pinning forces F_P for the double-doped sample are 12.8 GN/m³ at 77K, 46.3 GN/m³ at 65K, and 122 GN/m³ at 40K. In the double-doped sample, the angular dependence of J_c showed a broad peak at B//c due to the flux pinning by c-axis correlated defects, combined with a plateau, due to the flux pinning by isotropic pinning centres. Consistently, both BaZrO₃ nanorods parallel to the c-axis and Y₂O₃ nanoparticles randomly dispersed inside the YBCO matrix were observed in TEM images.