Recently, the BaHfO 3 (BHO) nanorod has attracted attention as a new c-axis-correlated pinning center in REBa 2 Cu 3 O y films. We fabricated SmBa 2 Cu 3 O y (SmBCO) films with BHO nanorods using an alternating-targets technique with pulsed laser deposition on single-crystal LaAlO 3 (100) substrates, and then compared the microstructure and flux pinning properties with those of BaSnO 3 (BSO)-doped SmBCO films. Transmission electron microscopy observations indicated that the BHO and BSO nanorods both grew straight, but the inclination of the BHO nanorods from the c-axis of the SmBCO was less than that of the BSO nanorods. The inclination had a strong influence on the flux pinning property. The flux pinning force of the BHO-doped SmBCO film (F MAX p = 28.0 GN m −3 with J c = 2.0 MA cm −2 at 77 K under 1.4 T) became stronger than that of the BSO-doped SmBCO film (F MAX p = 24.5 GN m −3 with J c = 1.4 MA cm −2 at 77 K under 1.8 T) due to the shape of the BHO nanorods without inclining.

YBa 2 Cu 3 O 7−x + BaSnO 3 (YBCO + BSO) mixed films with increasing BSO content were prepared on SrTiO 3 substrates by pulsed laser deposition from YBCO + x wt% BSO mixed targets (x = 2, 3, 4, 5, 6, 8 and 9 wt%). Transmission electron microscopy (TEM) images reveal that BSO is incorporated into the YBCO matrix in form of nanorods, whose density and size increase with increasing BSO content. The pinning properties for the mixed YBCO + BSO film were systematically studied. The 4 wt% sample presents the maximum global pinning forces F P at all considered temperatures: 28.3 GN m −3 near 2 T at 77 K, 103 GN m −3 near 5 T at 65 K, and >241 GN m −3 near 9 T at 40 K.

We introduced high density columnar defects, as artificial pinning centres (APCs) for quantized vortices, into YBa 2 Cu 3 O 7−x (YBCO) films during the film deposition procedure. APCs were introduced perpendicular to the film surface using nanosized Y 2 O 3 islands prepared on SrTiO 3 (100) substrates by pulsed laser deposition. Varying the deposition parameters and the substrate annealing conditions allowed strong changes in the shape and density of the Y 2 O 3 islands to be induced. The best performance among the APC samples as compared to the pure YBCO film was obtained for that grown on the Y 2 O 3 -deposited substrate with five laser pulses, corresponding to 0.2 Y 2 O 3 monolayers (ML). Even when the 0.2 ML APC films were prepared using the same deposition conditions, the columnar defects enhanced J c at 77 K from 1.8 to 2.7 MA cm −2 (self-field) and from 0.06 to 0.10 MA cm −2 (H = 5 T).

YBa2Cu3O7−x+Y2O3 (YBCO+Y2O3) mixed films were prepared on SrTiO3/MgO substrates by pulsed-laser deposition from a YBCO target with a thin Y2O3 sector on the top. The pinning properties for the mixed YBCO+Y2O3 thin film were strongly enhanced, especially at the temperatures lower than 77 K: the maximum global pinning forces FP for the Y2O3 doped sample are 7.8 GN m−3 near 2 T at 77 K, 54.5 GN m−3 near 4 T at 65 K, and 189 GN m−3 near 9 T at 40 K. In the Y2O3-added samples, except for the plane configuration, the angular dependence of Jc showed a plateau, due to the flux pinning by isotropic pinning centres. Y2O3 nanoparticles randomly dispersed inside the YBCO matrix were consistently observed in the cross-sectional TEM images.