In situ study of equilibrium phenomena and kinetics in a BiSCCO/Ag tape

Structural changes during the annealing of a mono-filament BiSCCO/Ag tape in air are monitored in situ by synchrotron X-ray diffraction. Starting at 750°C, a very slow ramp rate is used, followed by high temperature cycling to study equilibrium phenomena and kinetics. For the first time, the concentration of the partial liquid is directly monitored. A 3321 phase dissolves below 790°C. Between 760°C and 820°C, the 2212 lattice parameters contract, indicating incorporation of Pb and/or Ca. At the same time, grain growth takes place, relieving strains. Between 820°C and 840°C (Ca,Sr) 2PbO 4 dissolves incongruously, while the amount of liquid increases. Conversion of 2212 to 2223 takes place at all temperatures above 820°C. Above 833°C, (Ca,Sr) 2CuO 3 appears. Cycling between 845°C and 860°C—where 2212 has almost disappeared—reveals fast, nearly reversible changes, indicative of several eutectics involving the 2212, 2223, (Ca,Sr) 2CuO 3 and liquid phases. By cycling, the incorporated Ca and/or Pb is lost irreversibly. Cooling data are consistent with precipitation of 2212 and 2223 by layer-on-layer growth on the existing grains. Some comments on growth models and a comparison to similar annealing experiments with constant operation temperature are given.