Title :
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//
Author :
Crossley, A. ; Li, Y.H. ; Caplin, A.D. ; MacManus-Driscoll, J.L.
Author_Institution :
Centre for High Temp. Supercond., Imperial Coll. of Sci., Technol. & Med., London, UK
fDate :
6/1/1999 12:00:00 AM
Abstract :
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.
Keywords :
bismuth compounds; calcium compounds; critical current density (superconductivity); flux pinning; high-temperature superconductors; lead compounds; strontium compounds; superconducting tapes; (Bi,Pb)-2212 stability line; Bi/sub 2.2-x/Pb/sub x/Sr/sub 1.8/CaCu/sub 2/O/sub 8+/spl delta//; Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8/:Pb; Pb solubility; coulometric titration system; flux pinning; grain formation; high Pb doping; high temperature superconductor; intra-granular critical current density; melt-processed; nanoscale precipitates; phase formation; poorer texture; reduced grain sizes; screen-printed (Bi,Pb)-2212 tapes; Annealing; Bismuth; Control systems; Doping; Flux pinning; Isothermal processes; Oxygen; Pressure control; Stability; Strontium;
Journal_Title :
Applied Superconductivity, IEEE Transactions on
