The effect of high Pb doping on phase stability of Bi1.6Pb0.6Sr1.8CaCu2O8+δ and on microstructure and pinning in Bi1.6Pb0.6Sr1.8CaCu2O8+δ/Ag tapes

The Bi2.2-xPbxSr2CaCu2O8+delta ((Bi, Pb)-2212) stability line has been measured for a Pb doping level, x, of 0.6, using a coulometric titration (CT) system between 700 degrees C and 840 degrees C, and for the range 10(-5) atm < pO(2) < 3 x 10(-2) atm. The supersolidus decomposition reaction was determined to be (Bi, Pb)-2212--> L + (Sr, Ca)CuO2 + CaO. This is different to partial melting of Pb-free Bi-2212 under similar conditions, where the liquid, L, is more Cu poor, and where only one solid phase, (Sr, Ca)(2)CuO3, forms. In order to ascertain whether a high Ph concentration leads to enhanced values of J(c) in a practical conductor, the derived thermochemical information was utilized to melt process Bi1.6Pb0.6Sr2CaCu2O8+delta tapes. Optimum phase purity was obtained by processing at 800 degrees C, and 2.3 x 10(-3) arm < pO(2) < 2.8 x 10(-3) arm, using a step isothermal-isobaric processing route. A Pb concentration of x = 0.4 was obtained within the (Bi, Pb)-2212 grains. However, small grain sizes and poor texture were obtained through the thickness of the tapes. The intra-granular critical current density (J(c)) of the (Bi, Pb)-2212 platelets was found to be approximately the same as that measured in melt processed, Ph-free Bi-2212.