The glass formation, thermal stability and phase separation, some phys ical properties including electrical conductivity, crystallization behaviors in Bibased precursor glasses such as Bi2Sr2CaCu20x and Bil.6Pb0.4Sr2Ca2Cu3Ox, and formation mechanism of superconducting crystals have been clarified, A key factor for an understanding for these points is the copper valence state, i.e. the ratio of Cu + and Cu 2+ , because the coordination state of Cu + and Cu 2+ in Bibased glasses might be largely different. The crystallization mechanism and kinetics are strongly affected by oxidation behaviors of Cu + to Cu 2+ .

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The formation mechanism of the high-To phase through the glass-ceramic route and the role of Pb on the formation of this phase have been investigated. It was found that a new compound with the chemical composition Pb2Sr3 xCaxCuOv (x = 1.8) precipitates at around 550°C. This phase is stable up to 800°C, where it begins to decompose, and at 850°C it completely disappears. It was found that some part of the released Pb diffuses into the 2212 phase leading to the formation of Pb-containing 2212 phase, (Bi,Pb)2Sr2CaCu2Ox. On the other hand, an endothermic peak, probably arising from the melting of (Bi,Pb)2Sr2CaCu2Ox phase or melting at grain boundaries containing Pb 2+, was observed at 856°C only in Pb-containing samples that were heat treated. The liquid phase attributed to the endothermic peak may enhance the formation of high-Tc phase (2223 phase). The growth kinetics for the high-To phase were analysed using the Johnson-MehI-Avrami equation; the results indicate that the growth of the high-To phase is controlled by a diffusion process and the activation energy for its formation in the initial stage (shorter than 96 h) is 576_+45 kJ tool -1

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