High-efficiency preparation of high-quality YBCO superconducting films using an ultralow-fluorine sol-gel method

Superconducting YBa2Cu3O7-x (YBCO) films were prepared using an ultralow-fluorine sol with F/Ba = 2, which was synthesized using fluorine-contained barium trifluoroacetate (Ba-TFA), and fluorine-free yttium, barium, and copper salts. The mole ratio of F/Ba = 2 was realized in the sol by controlling the content of Ba-TFA. During the pyrolysis process, the fluorine-free and fluorine-contained Ba-salts were found to be completely converted to BaF2 phase, and almost no corrosive fluorinated gases (such as HF gas) were released out of the film, resulting in the film with smooth surface even under a high heating rate of 10-15 A degrees C/min. Single-coated YBCO film (similar to 280 nm) with critical current density (J(c)) of 5 MA/cm(2) (77 K, 0 T), and double-coated film (similar to 550 nm) with J(c) over 3.5 MA/cm(2) (77 K, 0 T) were obtained on LaAlO3 single crystal substrates. Compared with YBCO films deposited from solutions with higher fluorine content, the ultralow-fluorine sol-gel deposited YBCO films showed comparable superconductivity, but improved surface quality and production rate.