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 only the critical current density J/sub c/ anisotropy decreasing to a half as much as Pb free MgO doped crystals but J/sub c/ and irreversibility field B/sub irr/ improvement. Apparent pinning potential U/sub 0/* derived from flux creep experiments for these crystals also increased. Those results suggest that the effect of MgO doping is more pronounced by decreasing the J/sub c/ anisotropy of crystals. Dislocation increase in the Pb substituted Bi2212 crystals due to MgO doping was observed with a transmission electron microscope.