Structural origins of the properties of rare earth nickelate superlattices

NiO6 octahedral tilts in the LaNiO3/SrTiO3 superlattices are quantified using position averaged convergent beam electron diffraction in scanning transmission electron microscopy. It is shown that maintaining oxygen octahedra connectivity across the interface controls the octahedral tilts in the LaNiO3 layers, their lattice parameters and their transport properties. Unlike films and layers that are connected on one side to the substrate, subsequent LaNiO3 layers in the superlattice exhibit a relaxation of octahedral tilts towards bulk values. This relaxation is facilitated by correlated tilts in SrTiO3 layers and is correlated with the conductivity enhancement of the LaNiO3 layers in the superlattices relative to individual films.