STRONG FLUX-PINNING UP TO LIQUID-NITROGEN TEMPERATURE DISCOVERED IN HEAVILY PB-DOPED AND OXYGEN CONTROLLED BI2212 SINGLE-CRYSTALS

Heavily Pb-doped Bi2212 single crystals with carefully controlled oxyg en compositions were prepared and their magnetization curves were stud ied as a function of carrier doping level from heavily overdoped (T-c = 67 K) to near optimally-doped (T-c = 96 K) states. All the Pb-doped samples showed much improved J(c)-H properties compared to the convent ional Pb-free Bi2212 crystals. In particular, the moderately overdoped crystals maintained high J(c) and H-irr up to high temperatures and t hese values surpassed those for the Pb-ion irradiated Bi2212 with an o ptimized fluence. Dramatically improved flux pinning properties in the present material are possibly due to generation of temperature and fi eld-induced new pinning centers, as suggested by anomalous dependence of J(c) both on temperature and magnetic field. (C) 1997 Elsevier Scie nce B.V.