Effect of copper content in precursor solution on the superconducting properties of YBCO films derived from low-fluorine solution

Four low-fluorine solutions with different stoichiometry of Y:Ba:Cu = 1:2:ξ (ξ = 3, 3.5, 4, 4.5) were prepared using Ba-TFA, yttrium and copper acetate as precursors. YBa2Cu3O7−δ (YBCO) films derived from these low-fluorine solutions were coated on LaAlO3 (LAO) single crystal substrates by dip-coating process. The effect of copper stoichiometry in precursor solution on the microstructure and superconductivity of YBCO films was studied. The growth orientation and microstructure of the films were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The results show that there are large volume fraction of a-axis oriented YBCO grains in the films derived from precursor solutions with stoichiometry of Y:Ba:Cu = 1:2:ξ (ξ = 3, 3.5, 4.5), while the films from the solution with stoichiometry of Y:Ba:Cu = 1:2:4 mainly grow along c-axis orientation and the volume fraction of c-axis oriented grains is 96.33%. Superconductivity test indicate that the film derived from the precursor solution with stoichiometry of Y:Ba:Cu = 1:2:4 exhibits excellent superconducting properties with the critical transition temperature Tc approximate 90 K, the sharp transition temperature ΔT below 1 K and the critical current density Jc over 1 MA/cm2 (77 K, 0 T).