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Microstructure and properties of melt-processed Bi-2212 (Bi2Sr2CaCu2Ox)

Research paper by B. Heeb, L. J. Gauckler, H. Heinrich, G. Kostorz

Indexed on: 01 Oct '93Published on: 01 Oct '93Published in: Journal of Electronic Materials



Abstract

Microstructural development and properties during melt processing of Bi-2212 were investigated with regard to the production of superconducting oxides in bulk shape for the application in electrical engineering. Oxygen loss during heating and melting leads to incongruent solidification on cooling and therefore multiphase microstructures. Phase compositions depend on oxygen stoichiometry, which is determined by oxygen partial pressure, maximum sintering temperature as well as cooling rate. During annealing, solid/liquid and subsequent solid/solid reactions yield high volume fractions of 2212. The oxygen absorption and the 2212 formation mechanism and its kinetics are strongly correlated. The11905→2212 transformation proceeds via intermediate states of high planar defect density and is promoted by frequent stacking faults, that allow diffusion of Ca- and Cu-atoms over short distance. Microstructures of the 2212 phase were also controlled by variations of the cation stoichiometry leading to an improvement of the superconducting properties.