Characteristics of ErBa₂Cu₃O_7-δ films with BaWO₄ doping

BaWO₄ (BWO) doped ErBa₂Cu₃O_7-δ (Er-123) (BWO + Er-123) films are fabricated and their superconducting properties are evaluated. We discuss the effect of BWO doping into Er-123 films on their crystallinity and superconducting properties. The grown BWO + Er-123 films were in-plane aligned and c-axis oriented. We characterize in-plane crystallinity of the films by XRD in-plane rotation measurement (φ-scan). The full width at a half maximum of the φ-scan pattern (δφ) of the grown BWO + Er-123 films became wider as increasing BWO doping. The critical temperature (T_C0) of 2.0 wt% BWO + Er-123 films was about 90.5 K. From this result, it was confirmed that the BWO + Er-123 films had as high T_C as pure Er-123 films. Surface resistance (R_S) of the BWO + Er-123 films was degraded comparing to that of a pure Er-123 film. The relationships between critical current density (J_C) and applied magnetic field (J_C-B) and the magnetic field angular dependence of J_C of the grown 2.0 wt% BWO + Er-123 film were evaluated at 77 K. As a result, it is confirmed that the J_C of the Er-123 films in magnetic fields decreased by the BWO doping comparing to that of the pure Er-123 film. However, it was also confirmed that the 2.0 wt% BWO + Er-123 film had weak pining centers along the c-axis of Er-123 films. From the result of a cross-sectional transmission electron microscope (TEM) image, some rod structures were observed in the 2.0 wt% BWO + Er-123 films. The diameter of the rod was about 20 nm. These rods grew along the c-axis of Er-123 films from the substrate to the surface of the film.