3. Stress Accommodation and Structural Distortions at Correlated Oxide Interfaces

Advances in atomically controlled synthesis of complex oxide heterostructures made possible to utilize the so-called strain engineering which enabled stabilization of new and unique structures at the oxide–oxide interfaces and in ultrathin films. Strain accommodation across the heteroepitaxial oxide interface is driven by different lattice parameters as well as by distinct crystallographic symmetry of the film and the substrate. Using advanced high-resolution X-ray diffraction (HR-XRD), we identified structural distortions at the heteroepitaxial interfaces and in ultrathin epitaxial perovskite oxide films that are induced by two distinct phenomena related to strain-octahedral coupling: lattice mismatch and interface symmetry mismatch. We show that unit cell distortions at the heteroepitaxial oxide interfaces significantly differ from structural distortions away from the interface region observed in thick coherent epitaxial oxide films. HR-XRD results reveal a formation of the novel structures at the interfaces between crystallographically dissimilar perovskite oxides. These structures are stabilized due to a unique coupling between octahedral rotations/deformations induced by symmetry mismatch and octahedral rotations due to lattice mismatch. The combination of crystallographic symmetry mismatch at the interface with the lattice mismatch offers new routes for strain engineering in functional complex oxide heterostructures that enables emergent physical phenomena and offer potential for future devices.