Microstructure and properties of MOCVD-derived Gd_xY_1−xBa₂Cu₃O_7−δ films with composition fluctuations

The effects of Gd content on crystalline orientation, microstructure and superconductivity of Gd_xY_1−xBa₂Cu₃O_7−δ (GdYBCO) films were systematically investigated. By varying the Gd content in the liquid precursor without changing the total amount of rare earth elements, series of GdYBCO films with x values of 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0 were fabricated by metal organic chemical vapor deposition (MOCVD). X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis revealed that Gd introducing could restrain the formation of CuYO₂ phase, but induce a-axis growth of GdYBCO film. The increase of x from 0 to 0.5 leads to enhancing critical current density at self-field and 77 K (J_csf) from 1.8 to 2.8 MA·cm⁻², which benefits from the decrease in CuYO₂ impurities and improvement of in-plane texture from 5.0° to 4.3°. However, raising x from 0.5 to 1.0 gives rise to abundant a-axis growth of film and degradation of in-plane texture from 4.3° to 5.4°, consequently resulting in the decrease of J_csf from 2.8 to 0.8 MA·cm⁻². Even though J_csf has not varied monotonically, the critical transition temperature of GdYBCO films linearly increases from 90.75 to 92.25 K and the in-field performance at magnetic field (B) of 0–1.1 T and 77 K as well as B parallel to film normal is also superior with Gd content increasing.