Fabrication of High-Quality Epitaxial YBCO Films Prepared by Fluorine-Free MOD

High-quality epitaxial YBa₂Cu₃O_7-δ (YBCO) films were successfully fabricated on LaAlO₃ (LAO) (001) substrates by fluorine-free metal-organic deposition (MOD). YBCO powder was dissolved into a fluorine-free source to prepare the coating solution. The solution was dip-coated on LAO, dried at 80°C for 10 min, pyrolized at the temperature up to 400°C in humid O₂ atmosphere, subsequently fired to produce YBCO in an oxygen partial pressure of 300 ppm, and finally oxygenated in a pure O₂ atmosphere at 450°C for 1 h. While, in addition to a-axis oriented grains, the formation of randomly oriented polycrystalline grains was unavoidable when as-pyrolized films were simply fired at 825°C for 2 h, high-quality epitaxial YBCO films with only a small amount of a-axis oriented grains were obtainable when as-pyrolized films were heated up to 850°C at first and then cooled down to 825°C and held for 2 h at the firing stage. Although our best YBCO film had a Tc,zero value of 87.5 K and Jc value of 0.47 MA/cm² at 77 K in a self-field at the present stage, this fluorine-free MOD is a promising alternative to conventional TFA-MOD since further improvement in Jc is possible through the processing optimization.