Pb substitution effects on the critical current density in MgO doped Bi2212 crystals

For heavily Pb substituted Bi2212 crystals with MgO doping, we found not on ly the critical current density J(c) anisotropy decreasing to a half as muc h as Pb free MgO doped crystals but J(c) and irreversibility field B-irr im provement, Apparent pinning potential U-0(*) derived from flux creep experi ments for these crystals also increased. Those results suggest that the eff ect of MgO doping is more pronounced by decreasing the J(c) anisotropy of c rystals. Dislocation increase in the Pb substituted Bi2212 crystals due to MgO doping was observed with a transmission electron microscope.