Nanostructural characterization of YBCO films on metal tape with textured buffer layer fabricated by pulsed-laser deposition

Abstract

Thick YBa2Cu3O7-x (YBCO) films with high critical current density (Jc) values were deposited by pulsed-laser deposition (PLD) on Hastelloy with a textured CeO2/Gd2Zr2O7 buffer layer. Both cross-sectional and plan-view TEM specimens of the YBCO films were prepared, and then the nanostructural characterization of the films was performed by transmission electron microscopy (TEM). The YBCO films less than 1 μm thick were predominantly composed of c-axis-oriented grains, however, many a-axis-oriented grains, which grew larger with the increase of the thickness of the YBCO film, were formed beyond about 1 μm from the CeO2 interface. We found Y2O3 and copper oxides between a- and c-axes-oriented grains. In particular, Y2O3 grains were formed between the {001} plane of an a-axis-oriented grain and the {100} or {010} plane of a c-axis-oriented grain. The orientation relationships between Y2O3 and YBCO are found to be; (001)YBCO//(001)Y2O3 and (100)YBCO//(110)Y2O3. In addition, we also found gaps between YBCO grains. Since a-axis-oriented grain growth and the formation of Y2O3, copper oxides and the gaps are considered to reduce the J c values of the YBCO film, it is important to determine the optimum process conditions to suppress the nucleation of a-axis-oriented grains, impurity oxides and gaps.