Structural study of nickelate based heterostructures

Heterostructures consisting of SmNiO₃ and NdNiO₃ alternating layers with additional LaAlO₃ spacer layers were grown and fully characterized by means of x-ray diffraction, atomic force microscopy, and scanning transmission electron microscopy. A change in the orientation of the orthorhombic long-axis of the nickelate layers is observed when a single unit cell of LaAlO₃ is inserted between SmNiO₃ and NdNiO₃, in agreement with density functional theory calculations. At the same time, the structure of the ultra-thin rhombohedral LaAlO₃ layers is affected by their proximity to orthorhombic nickelate layers, with both scanning transmission electron microscopy studies and density functional theory calculations revealing a weak antipolar motion of the La-cation in the LaAlO₃ layers that is not present in the bulk rhombohedral structure of this compound.