TRANSMISSION ELECTRON-MICROSCOPY STUDY OF MICROSTRUCTURE AND FINE A, B-AXIS-ORIENTED GRAINS AS FLUX-PINNING CENTERS IN C-AXIS-ORIENTED GDBA2CU3O7-X THIN-FILM

A thin film of GdBa2Cu3O7-x (GBCO) with mainly c-axis orientation prep ared by DC magnetron sputtering was examined by transmission electron microscopy. It was revealed that fine a, b-axis-oriented grains with a width of 6 to 15 nm were densely spread in the c-axis-oriented GBCO t hin-film matrix. The density is as high as 10(15) grains/m(3). Twins, dislocations, and translational grain boundaries were also observed in the film. Their densities are smaller than those of fine a, b-axis-or iented grains. CuOx particles with a large size coexisting with large a, b-axis-oriented grains were found, which may decrease the critical current density in the film. A high J(c) value was maintained even whe n the magnetic field was applied parallel to the c-axis of the GBCO fi lm. The angular dependence of the critical current density and a calcu lation result show that the boundaries between fine a, b-axis-oriented grains and c-axis-oriented grains are the key flux-pinning centers in the film.