Papers by Keyword: YBCO Superconductor

Abstract: polycrystalline Cu_xY_yO_z are made through solid state reaction. Ferromagnetism is found in this YCuO system at room temperature. The ferromagnetism quite probably originates from Cu₂Y₂O₅ , the Copper Yttrium Oxide. The average magnetic moment per Cu²⁺ is estimated to be 0.04μ_B. Itinerant electron magnetism is a rational explaination for the observed ferromagnetism. The experiment shows that the excessive amount of Cu may lead more defects and further distortion in the lattice and decrease the exchange interaction. This reminds us that the Copper Yttrium Oxide is a substance not only should be avoided in fabricating YBCO superconductors but also should be considered as a potential substance of magnetic semiconductor.

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The effects of gamma ray irradiation on high temperature superconductors YBa₂Cu₃O_7-δ with nano particles Fe₃O₄ (20-30 nm) addition were investigated. YBCO superconductor powders were prepared by using high purity oxide powders via solid state reaction method. 0.01 – 0.05 wt.% of nano particles were added into YBCO. Samples were irradiated with 100 kGy gamma ray. The critical temperature (T_c) and transport critical current density (J_c) were determined by using four point probe method. The lattice parameters and morphology of the samples were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM), respectively. The results before and after gamma ray irradiation were compared. All of the samples showed increased T_c-zero after 100 kGy gamma ray irradiation. However, the J_c was degraded after gamma ray irradiation. There is no significant variation found in the XRD patterns. The porosity of the samples was increased by the gamma ray irradiation. It can be concluded that gamma ray irradiation has enhanced the superconducting properties but degraded the transport properties.

Abstract: YBCO (YBa₂Cu₃O₇/ Y₂BaCuO₅) bulk single-grain superconductors were prepared by Top-Seeded Melt-Growth (TSMG) process. CeO₂, BaCeO₃ and BaO₂ powders were added to nominal composition Y_1.5Ba₂Cu₃O_y (Y-123) with the aim to refine Y₂BaCuO₅ (Y-211) secondary particles, which provide pining. Added powders were refined by friction milling. The system behaviour was characterized by thermal analyses. Microstructure of prepared samples was studied by polarized light microscopy and the influence of additions is described.

Abstract: The effects of NiO nanoparticles addition in YBa₂Cu₃O_7-δ (YBCO) superconductors had been investigated. YBCO superconductor powders were prepared by using high purity oxide powders via solid state reaction method. 0.01 0.05 wt.% of NiO nanoparticles were added into YBCO. The critical temperature (T_c) and transport critical current density (J_c) were determined by using four point probe method. The lattice parameters and morphology of the samples were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM), respectively. T_c of YBCO increased from 84 K to 87 K with 0.02 wt.% of NiO nanoparticles addition. The addition on NiO nanoparticles have significantly enhanced transport critical current density of YBCO by acting as flux pinning centers. YBCO with 0.03 wt.% of NiO nanoparticles performed the highest J_c up to 1265 mA/cm² among the NiO-added samples. However, excessive addition of NiO nanoparticles in YBCO caused degradation in T_c and J_c.

Abstract: The effects of nano particles Fe3O4 addition on the superconducting and transport properties of YBa2Cu3O7-δ (YBCO) were studied. YBa2Cu3O7-δ superconductor powders were prepared by using high purity oxide powders via solid state reaction method. Nano Fe3O4 with 0.01 – 0.05 wt.% with average size 28 nm was added into YBCO. The transition temperatures (Tc) of the samples were measured by using four point probe method. The critical current (Ic) of the samples has been determined by using the 1 μV/cm criterion from 30 – 77 K. Sample with 0.02 wt.% nano Fe3O4 showed the highest Tc at 87 K. It is interesting to note the same sample also exhibited the highest Jc at 77 K up to 1683 mA/cm2. Nano Fe3O4 has acted as effective flux pinning centers in YBCO. A small amount of nano particles Fe3O4 addition has successfully improved the superconducting and transport properties of YBCO. The excessive addition of nano Fe3O4 (> 0.02 wt.%) suppressed the Tc and Jc. Overall, Jc decreases with increasing temperature (30 – 77 K) as a consequence of thermally activated flux creep. Magnetic impurities normally suppress superconductivity. However, by adding magnetic nano particles, current carrying capacity of superconductors YBCO was enhanced significantly.