Formation of dislocations via misfit strain across interfaces in epitaxial BaTiO₃and SrIrO₃heterostructures

Dislocations often occur in thin films with large misfit strain as a result of strain energy accumulation and can drastically change the film properties. Here the structure and dislocations in oxide heterostructures with large misfit strain are investigated on atomic scale. When grown on SrTiO₃(001), the dislocations in both the monolithic BaTiO₃thin film and its superlattices with SrIrO₃appear above a critical thickness around 6 nm. The edge component of the dislocations is seen in both cases with the Burgers vector of⟨100⟩. However, compared to monolithic BaTiO₃, the dislocation density is slightly lower in BaTiO₃/SrIrO₃superlattices. In the superlattice, when considering the SrTiO₃lattice constant as the reference, BaTiO₃has a larger misfit strain comparing with SrIrO₃. It is found that in both cases, the formation of dislocation is only affected by the critical thickness of the film with larger lattice misfit (BaTiO₃), regardless of the existence of a strong octahedral tilt/rotation mismatch at BaTiO₃/SrIrO₃interface. Our findings suggest that it is possible to control the position of dislocations, an important step toward defect engineering.