Introduction and control of Y2O3 nanoparticulate defects in YBa2Cu3O7-x films

メレパオロ, 松本要（九工大）；一瀬中（電中研）；向田昌志（九大）；吉田隆（名大）；堀井滋（東大）
pmele*post.matsc.kyutech.ac.jp

Abstract:YBa2Cu3O7-x＋Y2O3 （YBCO＋Y2O3） mixed films were prepared on SrTiO3 substrates by pulsed-laser deposition A thin （0.5 mm thick） and narrow （its area is about 2.5% of the surface area of YBCO target） Y2O3 sector was cut from an Y2O3 single crystal, and stuck on the YBCO target by silver paint, which is a very easy fabrication technique.We found that the pinning properties of YBCO＋Y2O3 mixed 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/m3 77 K, 54.5 GN/m3 at 65 K, and 189 GN/m3 at 40 K. Except for the B//ab axes 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. In a foll! owing series of experiments, the density of Y2O3 nanoparticles in YBCO films was controlled by varying the area of Y2O3 sector stuck on YBCO target. The optimum Y2O3 addition for Fp improvement in magnetic fields was found to be around 5.4 A%. For this sample, FP is approaching 14 GN/m3 at 77 K, as same as reached in YBCO added with BaZrO3 nanorods, but almost without any depression on superconducting critical temperature. The results indicate that the further increase in Fp is possible and is high-impact goal to be pursued, together with finding the maximum pinning force that can be achieved in high magnetic fields.