COMPOSITIONAL EFFECTS IN YXBAYCUZO7-DELTA THIN-FILMS PREPARED BY METALORGANIC CHEMICAL VAPOR-DEPOSITION

We report on effects of composition onto superconducting and structural properties of Y-Ba-Cu-O thin films, prepared by a carrier-gas free metalorganic chemical vapor deposition technique. Thin films with critical temperatures T(c) greater-than-or-equal-to 90 K, transition widths DELTAT(c) less-than-or-equal-to 1 K, and critical current densities j(c) (T=77 K, B=0 T) greater-than-or-equal-to 10(6) A/CM2 can be prepared by this method. Here we report on a strong dependence of the T(c) on the ratio of Ba/Cu. For Ba/Cu < 2 the surfaces show CuO precipitates, increasing in quantity and size with increasing concentration of Cu. An excess of Y leads to oriented inclusions of cubic Y2O3. A deficit of Y and Cu causes an expansion of the c-lattice parameter. To investigate the influence of Y2O3 and CuO precipitates on the pinning potential, resistive transitions in magnetic fields up to 12 T were measured and interpreted by a thermal activated flux-creep model. These measurements indicate. the inefficiency of both, inclusions and precipitates, on the enhancement of the pinning potential.