抄録
The critical current densities of the oxide high-TC superconductors obtained so far are not sufficient for practical application. In addition to the strong anisotropy in superconducting properties, there are several factors that determine the JC of the oxide superconductors, which are weak link at grain boundaries, flux pinning mechanism, and flux creep. In this review paper, our recent results for intergrain coupling and flux creep in Bi- and Tl-based materials are presented. The grain alignment in Bi-Pb-Sr-Ca-Cu-O material, which can be achieved by tape processing techniques, has been found to improve the intergrain coupling and also the flux creep problem. The resistivity vs. temperature curves in magnetic fields measured for Tl-Ba-Ca-Cu-O single crystal indicates an exponential temperature dependence of the resistivity at lower resistivity region, suggesting that the resistivity occurrence is due to the thermally activated flux motion.
