Reaction Mechanism of Forming the High-Tc Superconductor in the Pb-Bi-Sr-Ca-Cu-O System

A relationship between synthesized phases and starting compositions has been studied in the Pb-Bi-Sr-Ca-Cu-O system. The reaction step of forming the high-T c phase (T c∼110 K) has been presumed as follows. Firstly, the high-T c phase and Bi2Sr2CuO x are obtained from the disproportionation reaction of the low-T c phase. Bi2Sr2CuO x and residual Ca and Cu atoms melt into the PbO flux. The low-T c phase is precipitated from the melt. The formed low-T c phase causes a further disproportionation reaction. The high-T c phase is produced in large quantities by repeating the cycle.