MICROSTRUCTURE AND PROPERTIES OF MELT-PROCESSED BI-2212 (BI2SR2CACU2OX)

Microstructural development and properties during melt processing of B i-2212 were investigated with regard to the production of superconduct ing oxides in bulk shape for the application in electrical engineering . Oxygen loss during heating and melting leads to incongruent solidifi cation on cooling and therefore multiphase microstructures. Phase comp ositions depend on oxygen stoichiometry, which is determined by oxygen partial pressure, maximum sintering temperature as well as cooling ra te. During annealing, solid/liquid and subsequent solid/solid reaction s yield high volume fractions of 2212. The oxygen absorption and the 2 212 formation mechanism and its kinetics are strongly correlated. The 11905underbar-->2212 transformation proceeds via intermediate states o f high planar defect density and is promoted by frequent stacking faul ts, that allow diffusion of Ca- and Cu-atoms over short distance. Micr ostructures of the 2212 phase were also controlled by variations of th e cation stoichiometry leading to an improvement of the superconductin g properties.