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

自从发现高T_c超导体以来，已经有十多年了。并且由于大量的研究和发展，它们的一些实际和商业用途已经开始，即用于无液氦超导磁体的线圈和电源线电缆。然而，目前发展起来的超导氧化物材料，如铋基带，在高温、高场下都没有良好的钉接性能和较高的临界电流密度。因此，它们在大电流和磁场中的应用被认为是困难的，基于不同系统的导线材料的开发至关重要。氢基氧化物超导体的T_c为135K，创历史新高，但传统的合成方法难以制备，且化学性质不稳定，因此我们集中精力研究如何通过化学修饰来增强其稳定性，提高其临界电流密度，以便于实际应用。此外，我们还尝试提高铋基超导体的磁通钉接性能和临界电流密度。结果表明，Re取代Hg位点增加了化学稳定性，同时也增加了不可逆性场。此外，在与日本京都大学团队的合作过程中，我们发现重掺杂Pb对铋基超导体的磁钉钉性能有显著的改善。我们仍在继续研究开发以Hg-和bi系统为主要基础的下一代线材，在本研究项目中，我们成功地实现了化学稳定和钉接性能的增强，并建立了各种液氮温度下长线材的加工工艺。

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.