The influence of high Pb doping on flux pinning and phase formation in bulk and tapes of Bi/sub 2.2-x/Pb/sub x/Sr/sub 1.8/CaCu/sub 2/O/sub 8+/spl delta//

The effect of oxygen partial pressure on Pb doping in Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// (Bi-2212) and its influence on flux pinning in bulk and tape materials has been investigated. Oxygen partial pressure was controlled precisely using a coulometric titration system. Bulk Bi/sub 2.2-x/Pb/sub x/SrCaCu/sub 2/O/sub 8+/spl delta// ((Bi,Pb)-2212) was annealed just above the (Bi,Pb)-2212 stability line in order to maximise the level of Pb doping. Screen-printed (Bi,Pb)-2212 tapes were melt-processed using a combination of isothermal and isobaric steps. In the bulk material the effect of Pb-doping on defect formation and intra-granular critical current density (J/sub c/) was investigated, and in the tapes the influence of Pb on (Bi,Pb)-2212 grain formation and J/sub c/ was studied. Pb solubility was found to increase with decreasing oxygen partial pressure (pO/sub 2/) and Pb levels of up to x=0.6 for Bi/sub 2.2-x/Pb/sub x/Sr/sub 1.8/CaCu/sub 2/O/sub 8+/spl delta// were incorporated at low pO/sub 2/ in both bulk and tape samples. The bulk samples showed nanoscale precipitates of (Bi,Pb)-2212 embedded in the (Bi,Pb)-2212 matrix. In the melt processed tapes, the high Pb levels led to reduced grain sizes and poorer texture. J/sub c/ values were not enhanced through incorporation of high levels of Pb.