Microstructures of YBa2Cu3O7-x films prepared by low-pressure oxygen atmosphere post-annealing of precursor films using Y, BaF2 and Cu

Transmission electron microscopy (TEM), reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) are used to characterize the microstructure and surface topography of YBa₂Cu₃O_7-x (YBCO) films. The YBCO films of approximately 0.2 and 0.8 μm thickness are prepared by a post-annealing of precursor films of co-evaporated Y, BaF₂ and Cu. The annealing conditions are the same for all cases except for the temperature elevation rate. RHEED patterns corresponding to the YBCO structure are observed in both the samples after annealing at 700 °C for 30 minutes. The XRD patterns show that both YBCO films have primarily c-axis orientation. According to TEM observation results, the YBCO film of 0.2 μm thickness is epitaxially grown from a substrate surface. In the case of thicker films of 0.8 μm, the bottom region of the film is epitaxial YBCO, while the top region is a mixture of a-axis orientation, other orientations and impurities.