Improvement of the pinning property in YBa2Cu3O7− x films below 35 K by doping with graphene oxide

Pinning induction in REBa2Cu3O7−x (RE = rare earth) films and coated conductors improves their critical current density (Jc). In general, however, interstitial elements, e.g., C and N, cannot act as effective pinning centers in REBa2Cu3O7−x materials because they typically lead to degeneration of the superconducting properties. In this work, the influence of graphene oxide (GO) on YBa2Cu3O7−x (YBCO) films was studied by measuring the critical temperature and angle-dependent critical current density. The results revealed that the concentration of GO in YBCO films modulated the critical temperature. The decay rate of Jc in H∥c field orientations decreased with decreasing temperature. At 35 K and 4.2 K, the YBCO/GO film exhibited a lower decay of Jc and less anisotropic behavior than the YBCO-BaMO3 (M = Zr, Hf) film. GO doping could, therefore, improve the pinning property of YBCO films below 35 K. This improvement could be due to the presence of nanosized carbon structures, which served as isotropic pinning centers at low temperature, as revealed by high-resolution transmission electron microscopy.