Preferred alignment of twin boundaries in YBa2Cu3Ox thin films and YBa2Cu3Ox/PrBa2Cu3Ox superlattices on SrTiO3

The structure of YBa2Cu3Ox thin films and YBa2Cu3Ox/PrBa2Cu3Ox superlattice films grown on (00L) SrTiO3 substrates has been studied using x-ray diffraction and transmission electron microscopy. The films consist of four symmetry-equivalent domains related by mutually perpendicular (hh0) and (hh̄0) twin boundaries. One twin orientation is often highly favored over the other. We have correlated this in-plane symmetry breaking with small miscuts of the substrate surface towards the [HH0] direction and propose that interfacial steps act as nucleation sites for twins. Thus, by controlling the surface normal, a technique is described for producing films containing aligned twin boundaries.