Stabilisation of the 110 K phase in Pb-substituted Bi-Sr-Ca-Cu-O

A number of samples of Bi_2-xPb_xSr₂Ca₃Cu₄O_y (0<or=x<or=0.8) have been prepared by solid state reaction. All major peaks in the powder diffraction spectra of samples with x=0.2 and 0.4 could be attributed to the Bi₂Sr₂Ca₂Cu₃O_y phase with slight orthorhombic distortion. Resistivity measurements of these samples showed zero resistance at 100 K with onset of superconductivity around 110 K. The effect of variations of sintering and annealing have been studied in order to optimize conditions for obtaining the 110 K phase. From flux exclusion measurements the volume fraction of the high-T_c phase is estimated to be around 40% at best. These studies tentatively indicate that Pb substitutes preferentially on the Ca site rather than the Bi site in the Bi-Sr-Ca-Cu-O lattice. Samples with x=0.0 and x>0.4 showed zero resistance around 70 K with no indication of a phase with a higher T_c.