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 YBa2Cu3O7-delta (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 Delta T deduced from the R-T curve is less than 1 K; the critical current density J(c) is 1.65 MA/cm(2) (77 K, 0 T), as tested by an electric transport method, and 1.83 MA/cm(2) (77 K, 0 T), as measured by magnetization measurement.