Growth mechanisms and properties of 90 degrees grain boundaries in YBa2Cu3O7 thin films.

Abstract

The transport properties of three types of 90\ifmmode^\circ\else\textdegree\fi{} 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\ifmmode^\circ\else\textdegree\fi{} off-axis sputtering are compared. A simple description of the in-plane crystallographic film orientation is given by substrate [010]\ensuremath{\parallel}YBCO[010] and substrate [1\ifmmode\bar\else\textasciimacron\fi{}01]\ensuremath{\parallel}YBCO 〈301〉. A domain structure exists with the ${\mathrm{CuO}}_{2}$ planes oriented at \ifmmode\pm\else\textpm\fi{}45\ifmmode^\circ\else\textdegree\fi{} to the substrate surface (i.e., parallel to the substrate [010] direction). Therefore, specific sets of 90\ifmmode^\circ\else\textdegree\fi{} 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.