Enhancement of Critical Current Density of Hg-Based High Tc Superconductors and their application

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It has been over ten years since the discovery of high T_c superconductors. And as a result of numerous researches and developments, some practical and commercial use of them have begun, i.e., coils and power lead cables for the liquid-helium-free superconducting magnets. Superconducting oxide materials developed so far, such as Bi-based tapes, however, don't have good pinning properties and high critical current density at high temperature and under high field. Therefore, their applications for high current and field are considered to be difficult, and developments of wire materials based on different systems are crucial.Hg-based oxide superconductor has the record high T_c,135K,but is difficult to make by the traditional synthesis method and considered to be chemically unstable, So we have concentrated our research efforts to intensify their stability by chemical modifications and increase their critical current density for practical use. Also, we have tried to enhance the flux pinning properties and the critical current density of the Bi-based superconductors.As a result, we have clarified that Re substitution for Hg site increases the chemical stability, and at the same time, the irreversibility field is increased, too. Also, in the course of collaborations with Kyoto University group, we have found the remarkable improvement of the flux pinning properties of the Bi-based superconductors by Pb heavy doping.We are still continuing our researches to develop the next-generation wire materials based mainly on the Hg- and Bi-systems, in which we have succeeded in chemical stabilization and pinning property enhancement in this research project, and to establish the processing procedures of the long wires for various applications at liquid nitrogen temperature.