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

高T_c超导体的发现已有十多年的历史。并且作为大量研究和开发的结果，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力引线电缆。然而，迄今为止发展起来的氧化物超导材料，如Bi系超导带材，在高温和高场下都不具有良好的钉扎性能和高的临界电流密度。Hg基氧化物超导体具有最高的Tc（135K），但传统的合成方法很难制备，且化学性质不稳定，因此，我们集中了研究的努力，以加强其稳定性的化学修饰和提高其临界电流密度的实际应用。此外，我们还试图提高Bi系超导体的磁通钉扎性能和临界电流密度，结果表明Re取代Hg位提高了化学稳定性，同时也提高了不可逆场。此外，在与京都大学的合作中，发现了Bi系超导体的磁通钉扎性能通过Pb重掺杂得到了显著改善。我们还在继续研究开发以Hg系和Bi系为主的下一代线材，在本研究项目中，我们成功地实现了化学稳定化和钉扎性能的增强。并建立在液氮温度下用于各种应用的长线材的加工程序。

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.