YBCO thin films prepared by fluorine-free polymer-based chemical solution deposition

We describe a new chemical solution deposition (CSD) route toward inexpensive and environmentally friendly preparation of YBCO coated conductors. This route is based on a fluorine-free polymer and exhibits some advantages compared to the TFA route, where trifluoroacetate precursors are used and aggressive HF is formed during the heat treatment. In this work, the main parameters influencing the structure and properties of YBCO films prepared by means of the polymer method are investigated. For the preparation of the YBCO films, stoichiometric amounts of Y, Ba and Cu nitrates were dissolved in a solution of polyacrylic acid in dimethylformamide. This metal polymer precursor solution was spin coated onto strontium titanate (STO) single crystals. After drying in air, the films were heat treated in an oxygen containing nitrogen atmosphere. The film structure was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). T_c and J_c were measured inductively. The preliminary results show that the amount of oxygen during heating and in the dwell time strongly influences the superconducting properties. Good superconducting properties, with T_c of 89.9 K (ΔT_c=1.1 K) and J_c of 10⁶ A/cm² at 77 K, have been obtained on epitaxially grown 250-nm-thick YBCO films using the polymer-based precursors.