Microstructure and Josephson phenomenology in 45 degrees tilt and twist YBa2Cu3O7-delta artificial grain boundaries

YBa2Cu3O7-delta (YBCO) artificial grain-boundary Josephson junctions have b een 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 degre es c-axis tilt or 45 degrees c-axis twist). A detailed characterization of the Josephson properties has been carried out, showing remarkable differenc es in the transport parameters of tilt and twist junctions. High-resolution electron microscopy showed the presence of perfect basal plane faced bound aries in the cross sections of tilt boundaries; however interfaces meanderi ng along the sample thickness are also sometimes observed. The correlation between transport properties and microstructure is investigated and the pos sibility to employ these junctions to explore the symmetry of the order par ameter is presented. On the basis of the analysis of microstructural data a nd of a qualitative growth model for (103) YBCO grains, it is suggested tha t clean basal plane boundaries exhibiting uniform Josephson properties coul d be obtained by this technique. [S0163-1829(99)01918-9].