| Co-Investigator(Kenkyū-buntansha) |
KISHIO Kohji The University of Tokyo, School of Engineering, Department of Applied Chemistry, Professor, 大学院工学系研究科, 教授 (50143392)
HORII Shigeru The University of Tokyo, School of Engineering, Department of Applied Chemistry, Assistant Professor, 大学院工学系研究科, 助手 (80323533)
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| Research Abstract |
In this study, we have attempted to improve critical current properties of superconductors for practical use and having layered crystal structure, such as RE 123 and Bi-based high-T_c cuprates and MgB_2, which has the highest re among the metallic superconductors, by the newly developed dilute impurity doping method. Introduction of weak superconducting regions with nm size, which can act as effective flux pinning sites, in the inherently strong superconducting matrix is the key concept of this method. We performed dilute impurity doping for various selected metal sites of the layered superconductors and systematically evaluated critical current properties of specimen.
For RE123 system, melt-solidified bulks were mainly used in this study. All the following dilute doping techniques, RE mixing, Sr or RE doping for Ba and Fe, Co, Ga or Ag doping for Cu in the CuO chain, were discovered to be effective for improving critical current density under magnetic fields. In particular, dilute doping for Cu in the CuO chain was most effective including thin film samples.
In the Bi-based cuprates, control of cation composition to be stoichiometric and achieving desirable carrier doping states, slightly overdoped - optimally doped, are found to be crucially important for high critical current performance. In addition, dilute RE doping for Ca or Sr sites of Bi(Pb)2212 single crystals dramatically enhanced J_c characteristics.
Above results mean that the dilute impurity doping for suitably selected site is universally effective method to improve critical current properties of cuprate superconductors. Furthermore, this method will be easily applied for development of high performance superconducting materials for practical applications.
For MgB_2 bulks, dilute Al doping improved J_c and addition of Ag decreased synthesis temperature. In additions, Yb and Lu were found to substitute Mg site. Moreover, mechanisms of improved critical current properties by C doping were clarified.
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