GROWTH MECHANISMS AND PROPERTIES OF 90-DEGREES GRAIN-BOUNDARIES IN YBA2CU3O7 THIN-FILMS

The transport properties of three types of 90-degrees grain boundaries of (103) oriented YBa2Cu3O7 (YBCO) thin films grown epitaxially on (101) SrTiO3 and (101) LaAlO3 substrates in situ by 90-degrees off-axis sputtering are compared. A simple description of the in-plane crystallographic film orientation is given by substrate [010]\\YBCO[010] and substrate [101]BAR\\YBCO [301]. A domain structure exists with the CUO2 planes oriented at +/-45-degrees to the substrate surface (i.e., parallel to the substrate [010] direction). Therefore, specific sets of 90-degrees grain boundaries are observed in both principal in-plane directions. The normal-state conductivity and the critical current density of these films along the YBCO [010] direction are as high as the best quality c-axis films, which have no high-angle grain boundaries. The normal-state conductivity and critical current density along the [301] direction are much lower than in the [010] direction. However, the normalized magnetic-field dependence of J(c) for both those directions is similar and shows no evidence of weak link behavior. These results have important implications for understanding the behavior of step-edge Josephson junctions. The anisotropic transport behavior in the normal and superconducting state is explained by the microstructure and a simple transport model.