Reaction Mechanism of High-Tc Phase (Tc=110 K) Formation in the Bi-Sr-Ca-Cu-O Superconductive System

Abstract
The reaction mechanism to produce the high-T c phase was investigated using X-ray powder diffractometry and thermogravimetry and differential thermal analysis (TG-DTA). The high-T c phase was produced through the low-T c phase (Bi2Sr3-x Ca x Cu2O y , 1<xT c phase. In order to produce the high-T c phase, it is necessary that the melting point of the low-T c phase be lower than that of the high-T c phase. Increase of Ca content in the low-T c phase or decrease of ambient partial oxygen pressure during calcination are quite efficient to decrease the melting point of the low-T c phase, and hence to enhance the formation of the high-T c phase.