The Formation of the High-Tc Phase in Pb-Doped Bi-Sr-Ca-Cu-O System

The microstructure on the formation of the high-T c phase was investigated in the Pb-doped Bi-Sr-Ca-Cu-O system. The high-T c phase was well stabilized for the composition of 1.4:0.6:2:2:3.6 for Bi:Pb:Sr:Ca:Cu. The fraction of the phase depends on the reaction time. At the early and intermediate stages of reaction, several phases such as Sr3-x Ca x Cu5O y , (Pb, Ca)-rich phase, the low-T c phase and high-T c phase were observed. At these stages, the low-T c phase was dominant. The low-T c phase was transformed into the high-T c phase through prolonged heat treatment, but a small amount of the low-T c phase and Sr3-x Ca x Cu5O y remained. The cation ratio in the high-T c phase was approximately 4:8:5:10 for (Bi, Pb):Sr:Ca:Cu.