Effect of Solution Composition on Superconducting Properties of YBCO Derived From TFA-MOD Process

The crystallization process of trifluoroacetate-metal-organic deposition derived YBa₂Cu₃O_7-y (YBCO) crystals has been investigated to understand the influence of the starting solution composition on the crystal growth process. The starting solutions with molar ratios of Y: Ba: Cu = 1.0: 2.0: 3.0 (stoichiometry) and 1.0:1.5:3.0 (Ba-deficient) were examined. The highest I_c values were achieved at 100 min holding time of the conversion step for 0.8- μm-thick YBCO films, which were independent of the starting solutions. The degradation of I_c performance was observed only in the films prepared from the stoichiometric solution with longer holding time than 100 min. The longer holding times for disappearing of the X-ray diffraction peak of BaF₂ derived from the stoichiometric solution is required compared to that from the Ba-deficient solution. On the other hand, the epitaxial growth rate measured from cross-sectional scanning electron microscopic observation for the YBCO films showed no difference between each other. X-ray diffraction analysis on the YBCO films fabricated from stoichiometric starting solution suggested that BaCuO₂ and/or Y₂O₃ phases formed during the solid-state reaction process. The degradation of I_c performance might be caused by the formation of BaCuO₂ phases.