The effects of target composition on the microstructure characteristic of epitaxial YBCO thin films by in-situ rf magnetron sputtering with single compound targets

The polycrystalline structure of epitaxial superconducting YBa2Cu3Ox(YBCO) thin films was studied using STEM/EDS and HREM. Two kinds of YBCO films with singificant difference in microstructure characteristic were found, which were prepared by rf magnetron sputtering with targets of different compositions, although both of samples showed with zero resistivity about 83K. These films were epitaxially grown on (001) MgO substrate and had the c-axis oriented. Impurity phases including CuO, Y2O3, Y2BaCuO5 (211) and very tiny precipitates were observed. The formation of impurity phase were dependent on the initial target composition. The precipitate of Y2O3 or 211 phase in films was found to have a special crystallographic relationship with YBCO matrix. The very tiny precipitates within YBCO matrix were believed to be responsible for the pinning centers. (orig.)