First-principles calculations of oxygen octahedral distortions in LaAlO3/SrTiO3 (001) superlattices
The size, shape and connectivity of oxide octahedron are essential for understanding and controlling the emergent functional properties of ABO3 perovskites. Using first-principles calculations, we systematically studied the oxygen octahedral rotation and deformation in LaAlO3/SrTiO3 (001) superlattices. Superlattices with electron- or hole-doped interfaces, or both, are compared. The results showed that there are at least three different types of oxygen octahedral distortions in these superlattices, which is more than had previously been reported in the literature. We demonstrate that interfacial oxygen octahedral coupling and hole-doping, in addition to epitaxial strain, are the key factors underlying the formation of multi-type oxygen octahedral rotations in these systems. We confirm that oxygen octahedral rotations and deformations play an essential role in insulator–metal transitions. Furthermore, to alleviate polar instability at the interfaces, polar distortions also occur in association with the oxygen octahedral deformation.