Evolution of the microstructures of melt-textured composites, under 100bar O at 600C, was monitored by means of transmission electron microscopy. Under these conditions, the Cu3Ba2YO7 phase extended out of its stability field and into a region of the phase diagram where the weakly superconducting Cu4Ba2YO8 polytype was stable against a CuO-Cu3Ba2YO7 mixture. The nucleation of 1/8<301> stacking faults was not restricted to the Cu3Ba2YO7/Y2BaCuO5 interfaces, as found in samples processed at 350 and 450C, but was strongly enhanced in the bulk matrix. At the same time, matrix decomposition into a Ba-Cu oxide, Y2BaCuO5 and probably CuO occurred at Y2BaCuO5 interfaces, and was accompanied by exaggerated growth of the stacking faults. After 12h under 100bar O at 600C, the entire volume imaged by transmission electron microscopy appeared to be covered with large stacking faults which overlapped along the c-axis. It was found that, when the Y2BaCuO5 interfaces became saturated with stacking faults, new stacking faults had to nucleate in the bulk matrix. Such isolated loops appeared to be arranged along lines parallel to <100>, close to neighbouring straight dislocations, and to be associated with twin boundaries.

Dislocation Substructures and Phase Stability of Melt-Textured YBa2Cu3O7-Y2BaCuO5 Composites at High Oxygen Pressures. J.Plain, F.Sandiumenge, J.Rabier, M.F.Denanot, X.Obradors: Philosophical Magazine A, 2002, 82[2], 337-48