  Considerable work has focused on the use of epitaxial strain to engineer
domain structures in ferroic materials. Here, we revisit the observed reduction
of domain variants in rhombohedral BiFeO3 films on rare-earth scandate
substrates. Prior work has attributed the reduction of domain variants to
anisotropic in-plane strain, but our findings suggest that the monoclinic
distortion of the substrate, resulting from oxygen octahedral rotation, is the
driving force for variant selection. We study epitaxial BiFeO3 DyScO3 (110)o
heterostructures with and without ultrathin, cubic SrTiO3 buffer layers as a
means to isolate the effect of symmetry mismatch on the domain formation. Two
variant stripe domains are observed in films grown directly on DyScO3, while
four-variant domains are observed in films grown on SrTiO3 buffered DyScO3 when
the buffer layer is >2 nm thick. This work provides insights into the role of
the substrate beyond just lattice mismatch in manipulating and controlling
domain structure evolution in materials.
