Chemical and Mechanical Stability of the High-Tc Phase in the Bi-Pb-Sr-Ca-Cu-o System (IV)—Formation of the High-Tc Phase in Amorphous Powder Prepared by Mechanical Grinding—

Chemical and mechanical stability of the high-Tc phase in the Bi-Pb-Sr-Ca-Cu-O system has been studied. In particular, the formation of the high-Tc phase has been discussed for samples of the amorphous powder with a composition of Bi_0.9Ph_0.2Sr_1.0Ca_1.0Cu_1.6O_z prepared by mechanical grinding. Annealing of the amorphous powder at low temperatures(500-800°C) leads to precipitation of some impurity phases. The Pb-rich low-Tc phase with an orthorhombic structure symmetry was found to form in samples of the amorphous powder heated at 820°C in air. The formation of the Pb-rich low-Tc phase seems to suppress the formation of the high-Tc phase in subsequent heat treatments at 850°C. Almost monophasic products of the high-Tc phase were obtained when the amorphous powder was heated at 840°C for 48h and subsequently at 850°C for 96h after calcination at 720°C.