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

We report on effects of composition onto superconducting and structura l properties of Y-Ba-Cu-O thin films, prepared by a carrier-gas free M O-CVD technique. Although high quality YBa2Cu3O7-delta thin films with T(c)ind greater-than-or-equal-to 90 K, DELTAT(c) less-than-or-equal-t o 1 K and j(c)trans (T=77 K,B=0 T) greater-than-or-equal-to 10(6) A/cm 2 C an be prepared by this method, one finds a strong dependence of th e inductively measured T(c)(50%) on the ratio of Ba/Cu. The surfaces s how CuO-precipitates for Ba/Cu < 2, increasing in quantity and size wi th increasing concentration of CuO. An excess of yttrium leads to cohe rent inclusions of cubic Y2O3 shown by X-ray diffraction and TEM-inves tigations, A ratio of Ba/Y > 2 causes an expansion of the c-lattice pa rameter, which qualitatively could be explained by a, ''cation-disorde r''-model. To investigate the influence of Y2O3- and CuO-precipates on the pinning potential, the resistive transition in magnetic fields up to 12T were measured and interpreted by a thermal activated flux-cree p model. These measurements indicate the inefficiency of both, inclusi ons and precipitates, to enhance the pinning potential.