Growth mechanisms and properties of 90° grain boundaries in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ thin films

The transport properties of three types of 90° grain boundaries of (103) oriented ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ (YBCO) thin films grown epitaxially on (101) ${\mathrm{SrTiO}}_3$ and (101) ${\mathrm{LaAlO}}_3$ substrates in situ by 90° off-axis sputtering are compared. A simple description of the in-plane crystallographic film orientation is given by substrate [010]∥YBCO[010] and substrate [1¯01]∥YBCO 〈301〉. A domain structure exists with the ${\mathrm{CuO}}_2$ planes oriented at ±45° to the substrate surface (i.e., parallel to the substrate [010] direction). Therefore, specific sets of 90° 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 ${\mathit{J}}_{\mathit{c}}$ 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.