Water-Vapor-Controlled Reaction for Fabrication of YBCO Films by Fluorine-Free Sol-Gel Process

Fluorine-free sol-gel process is a potential technique in preparing YBa₂Cu₃O_7-δ (YBCO) films due to avoiding the release of HF gas. In this paper, yttrium acetate, barium acetate, and copper acetate are used as the starting materials to synthesize a novel YBCO fluorine-free precursor solution. The phase evolution during the heat-treatment process of YBCO films and YBCO phase formation were studied, and the results show that the introduction of water vapor at the stage of high-temperature heat treatment can make the BaCO₃ phase become converted into the Ba(OH)₂ phase, which can be used as the barium source to react with CuO and Y₂O₃ to generate the YBCO phase, thus achieving the purpose for fabrication of high-performance YBCO films by fluorine-free sol-gel process. Through this approach, YBCO films with c-axis orientation and an excellent superconducting property can be obtained on a (001)-oriented LaAlO₃ (LAO) substrate. Superconducting property tests indicate that the superconducting critical transition temperature T_c is approximately 90 K, and the transition width T deduced from the R-T curve is less than 1 K; the critical current density J_c is 1.65 MA/cm² (77 K, 0 T), as tested by an electric transport method, and 1.83 MA/cm² (77 K, 0 T), as measured by magnetization measurement.