Microstructure and Josephson phenomenology in 45° tilt and twist YBa₂Cu₃O_7-δ artificial grain boundaries

YBa₂Cu₃O_7-δ (YBCO) artificial grain-boundary Josephson junctions have been fabricated, employing a recently implemented biepitaxial technique. The grain boundaries can be obtained by controlling the orientation of the MgO seed layer and are characterized by a misalignment of the c axes (45° c-axis tilt or 45° c-axis twist). A detailed characterization of the Josephson properties has been carried out, showing remarkable differences in the transport parameters of tilt and twist junctions. High-resolution electron microscopy showed the presence of perfect basal plane faced boundaries in the cross sections of tilt boundaries; however interfaces meandering along the sample thickness are also sometimes observed. The correlation between transport properties and microstructure is investigated and the possibility to employ these junctions to explore the symmetry of the order parameter is presented. On the basis of the analysis of microstructural data and of a qualitative growth model for (103) YBCO grains, it is suggested that clean basal plane boundaries exhibiting uniform Josephson properties could be obtained by this technique.