Microstructure of biepitaxial grain boundary junctions in YBa2Cu3O7

The microstructure of photolithographically defined 45° biepitaxial grain boundary junctions in YBa2Cu3O7 (YBCO) have been investigated by transmission electron microscopy. The junctions have been formed by growing YBCO and a buffer layer on a patterned MgO seed layer previously grown on r-plane sapphire or SrTiO3 coated (through the use of suitable buffer layers) (100) yttrium-stabilized-zirconia substrates. SrTiO3 or CeO2 buffer layers grown on these patterned MgO substrates reproduced the pattern with two variants crystallographically rotated 45° with respect to each other about the surface normal. The morphology of the YBa2Cu3O7 grown on these differently oriented patterned regions show marked differences; in particular, the ion milling damage to the sapphire surface during patterning causes the formation of low angle grain boundaries. The locations of the weak link grain boundaries with respect to the patterning in the MgO seed layer have been identified using electron diffraction.