High-T_c Phase Promoted and Stabilized in the Bi, Pb-Sr-Ca-Cu-O System

Partial substitution of Pb for Bi in the Bi-Sr-Ca-Cu-O system has been found to sharply increase the volume fraction of the high- T c phase when both the starting material (coprecipitated oxalate being used in the present study) and the heating process are appropriate. The sharp powder X-ray diffraction pattern obtained from well-grown particles, 5∼10 µm wide and 0.5 µm thick typically, was assigned to an orthorhombic cell with a =0.537 nm, b =2.682 nm, and c =3.726 nm. The electrical resistance dropped to zero at 107 K within the experimental limit of 10 -6 Ω. A large diamagnetic response in the ac susceptibility due to the Meissner effect was seen below 120 K. The dominance of the high- T c phase over the low- T c phase was roughly estimated at 9/1 in volume.