Fluorine-free sol–gel preparation of YBa2Cu3O7−x superconducting films by a direct annealing process

Using yttrium, barium and copper acetates as starting materials, fluorine-free YBCO precursor solution is prepared by the chemical complexation approach with diethylenetriamine, lactic acid, and α-methacrylic acid as complexing agents. Using the stable precursor solution, YBCO gel films are coated on LaAlO3 substrate by the dip-coating method. Effect of different heat treatment processes on the phase evolution and final film properties are examined. Results indicate that, either in a dry or in a humidified atmosphere, it is difficult to obtain high-performance YBCO films by a traditional pyrolysis–annealing process, due to the formation of stable BaCO3 phase during the pyrolysis process. On the contrary, using the fluorine-free precursor solution, epitaxial YBCO films with high Tc (>94 K) and Jc (>1 MA/cm2) can be obtained using a direct annealing process without pyrolysis process.