Effect of F/Ba ratio of precursor solution on the properties of solution-processed YBCO superconducting films

YBa₂Cu₃O_7−x (YBCO) thin films (with thickness of 220–230 nm) and thick films (with thickness of 1.1–1.2 µm) were prepared using low fluorine solutions with different F/Ba ratios (F/Ba=1–4.5). The effect of F/Ba ratio on the properties of the films was systematically investigated. The results showed that films derived from solutions with F/Ba<2, regardless of whether they were thin or thick, showed poor superconductivity due to the formation of BaCO₃ intermediate phase. When solutions with F/Ba≥2 were used, the superconductivity of as-prepared YBCO films was related to not only the film thickness, but also the F/Ba ratio in the solution. It was found that, for thick films derived from F/Ba>2 solutions, the formation of BaF₂/BaOF phase was retarded by the decomposition of Ba_1−xY_xF_2+x (BYF) intermediate phase. We also found that extra fluorine in the solution resulted in a large number of impurities and a-axis grains in the thick films, degrading the film superconductivity. F/Ba=2 was the optimal ratio in the solution to fabricate high-J_c YBCO thick films.