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 i n air are monitored in situ by synchrotron X-ray diffraction. Starting at 7 50 degrees C, a very slow ramp rate is used, followed by high temperature c ycling to study equilibrium phenomena and kinetics. For the first time, the concentration of the partial liquid is directly monitored. A 3321 phase di ssolves below 790 degrees C. Between 760 degrees C and 820 degrees C, the 2 212 lattice parameters contract, indicating incorporation of ph and/or Ca. At the same time, grain growth takes place, relieving strains, Between 820 degrees C and 840 degrees C (Ca,Sr)(2)PbO4 dissolves incongruously, while t he amount of liquid increases. Conversion of 2212 to 2223 takes place at al l temperatures above 820 degrees C. Above 833 degrees C, (Ca,Sr)(2)CuO3 app ears. Cycling between 845 degrees C and 860 degrees C-where 2212 has almost disappeared-reveals fast, nearly reversible changes, indicative of several eutectics involving the 2212, 2223, (Ca,Sr)(2)CuO3 and liquid phases. By c ycling, the incorporated Ca and/or Pb is lost irreversibly. Cooling data ar e consistent with precipitation of 2212 and 2223 by layer-on-layer growth o n the existing grains. Some comments on growth models and a comparison to s imilar annealing experiments with constant operation temperature are given. (C) 1999 Elsevier Science B.V. All rights reserved.