Generic positive effects of low level impurity doping on flux pinning properties of HTSC and MgB/sub 2/

Low level impurity doping effects on flux pinning properties have systematically studied for Bi(Pb)2212 single crystals, Y123 melt-solidified bulk and MgB/sub 2/ polycrystalline bulks. In all these systems, moderately dilute impurity doping was found to be effective for improving critical current properties without losing their original T/sub c/. For Bi(Pb)2212, iron, cobalt, nickel and yttrium were effective dopant for enhancement of J/sub c/ particularly under low fields. Second peak effect in J/sub c/-H properties of Y123 were observed in Sr doped Y123 bulk. These positive effects were happened only when mean distance of impurity ions was longer than the vortex core size, 2/spl xi//sub ab/. In the case of MgB/sub 2/, both aluminum doping for magnesium and carbon doping for boron improved J/sub c/ with their low doping levels less than 1%.