Nanoscale characterization of atomic positions in orthorhombic perovskite thin films

Abstract

The crystal structure determines many of the physical properties of oxide perovskites (ABO$_3$) and only a tiny modification of the lattice structure causes major changes in the functional properties through the interplay among spin, orbital and charge orders. The determination of characteristic distortions and symmetries is a valuable asset for understanding the structure-properties relationship and guiding the design of epitaxial oxide heterostructures, where electron degrees of freedom and correlated electronic states can be tailored. Even until new phases, otherwise absent in bulk materials, may appear. Here, we report on the in-depth structural characterization of 50~nm-LaVO$_3$ thin film grown onto (110)-oriented DyScO$_3$ by molecular beam epitaxy. We have investigated the heterostructure by means of x-ray diffraction, high-resolution and scanning transmission electron microscopies, scanning precession electron diffraction tomography and first-principle calculations. LaVO$_3$ crystallizes in the orthorhombic $Pbnm$ space group and is constrained by the substrate, which imposes a growth along the $[110]$ orthorhombic direction, over the 140 deposited unit cells. The mapping of the reciprocal space allows determining the orientation of the film and refining the lattice parameters. Using scanning transmission electron microscopy, we analyzed the structure of LaVO$_3$, focusing on the determination of the antipolar displacement of the rare earth. Additionally, 3D electron diffraction enabled to resolve the atomic positions of all species within the film.