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

Abstract

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 Sr_3-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 Sr_3-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.