High critical current density scheme of YBa₂Cu₃O_7−x films by the metalorganic deposition using trifluoroacetates

The formation of CuO nanocrystallite in a precursor has little influence on the critical current density (J_c) of the YBa₂Cu₃O_7−x (YBCO) film by the metalorganic deposition using trifluoroacetate. From the result of transmission electron microscopy, the microstructure of the YBCO film allows the coexistence of isolated CuO grains. Increasing humidity in the firing process is effective to decrease the grain growth of CuO nanocrystallite and attain high J_c of the films. We propose that a quasi-liquid is formed in a Cu-rich Y–Ba–O–F amorphous matrix and CuO/amorphous interface in the firing process with humidity. The quasi-liquid may help to diffuse H₂O and HF in the film during the firing process, therefore, the removal of HF gas from the film surface is only a growth limiting process. Such a growth scheme leads to high J_c with high reproducibility.