Heat treatment design of precursor solutions with different fluorine contents for YBa₂Cu₃O_7−x films through the sol-gel approach

The preparation of YBa₂Cu₃O_7−x (YBCO) film by low fluorine metal-organic deposition methodology has been extensively studied recently for its high efficiency and low cost. However, the relationship between the heating rate during pyrolysis and the fluorine content of precursor is still unclear and hence no universal thermal process has been widely accepted. In this work, we present the influence of different decomposition time for the YBCO films prepared by the precursor solutions with three F/Ba mole ratios of 6:1, 2:1, and 1:1 (the fluorine contents are 28.6, 9.5, and 4.8 % in the solutions, respectively). The similar X-ray diffraction (XRD) curves show that YBCO films with favorable c-axis oriented textures can be obtained by all the solutions and thermal processes. However, the ω-scan results and surface morphologies indicate that the film prepared by the low-fluorine solutions tend to deteriorate in out-of-plane orientation, but the surface morphologies are not easily wrinkled as the heating rates increase. J_c-B results show that the superior YBCO film with the J_c value up to 5.2 MA/cm² could be prepared by the precursor with the F/Ba mole ratio of 2:1 under the optimal decomposition process (a heating rate of 2 K/min). Considering the synergistic effect of the heating rate and fluorine content, a heat treatment strategy for obtaining satisfactory YBCO films was also proposed.