Practical Study On Fabrication And Properties Of YBCO HTS Tapes

Due to its lower ac loses, better in-field performance, high critical current, and extensive applications in the industry, YBCO High-temperature superconductor (HTS) tapes have attracted the attention of the researchers worldwide. In order to resolve sicentific and technical problems in fabrication and properties of YBCO HTS tapes, four fields were systematically studied in this dissertation:Preparation and electropolishing of non-magnetic Cu-Ni alloy substrates, preparation of CeO2/YSZ/Y2O3buffer layer, preparation of YBCO layer, and mechanical properties of YBCO tapes.1. Preparation and electropolishing of non-magnetic Cu-Ni alloy substratesHighly cube textured non-magnetic Cu-Ni alloy substrates were prepared by heavy rolling (reduction more than98%) and high temperature annealing (1000℃) method. It is found that increasing Ni content of the alloy, grading heating, controlling annealing temperature and time would improve the cube texture of the Cu-Ni alloy. The dissertation also explained the forming process of cube texture of the Cu-Ni alloy substrates. Electropolishing process was studied and minimum roughness of less than9nm was got on Cu-Ni alloy substrates. The mechanism of glycerin and additive was discussed. The effect of critical current and temperature on the polishing was also invesgated.2. Preparation of10-meter CeO2/YSZ/Y2O3buffer layer tapeHighly cube textured Y2O3seed layer and CeO2/YSZ/Y2O3buffer layer were fabricated by using DC reactive sputtering method. The buffer layers are smooth, dense and crac-free. The parameters of substrate temperature, total pressure, H2O pressure, and substrate moving speed were examined with respect to their role in the textureing process. A10-meter CeO2/YSZ/Y2O3buffer layer tape was obtained by using DC reactive sputtering method. The cube texture of the tape is uniform and surface of the tape is excellent.3. Preparation of meter-long YBCO HTS tapeA meter-long YBCO HTS tape was fabricated by using PLD method. Transition temperature (Tc) of88K, critical current density (Jc) of1.5MA/cm2(77K,SF), and critical current (Ic) of50A (2mm wide) were obtained. The parameters of substrate temperature, laser pulse repetition rate, annealing time, and substrate moving speed were examined with respect to their role in the formation of YBCO layer.4. Study of mechanical properties of YBCO tapes Residual stress of CeO2/YSZ/Y2O3buffer layer was measured and calculated using Substrate Curvature Method and Stoney Formula. The effect of total pressure and substrate temperature on the residual stress was studied. A residual stress theoretical model of CeO2/YSZ/Y2O3buffer layer was put forward. On the other hand, residual stress of YBCO layer was measured and calculated using Skew Symmetric Diffraction and Lattice Parameter method. The effect of film thickness on the residual stress and the effect of stress on the properties were studied. A residual stress theoretical model of YBCO layer was put forward too.