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Nanoscale characterization of atomic positions in orthorhombic perovskite thin films

M. Martirosyan, S. Passuti, G. Masset, J. Varignon, H. Chintakindi, J. Ghanbaja, S. Migot, A. Benedit-Cardenas, L. Pasquier, K. Dumesnil, L. Palatinus, W. Prellier, A. David, Ph. Boullay, O. Copie

TL;DR

This work addresses how nanoscale lattice distortions in orthorhombic perovskites influence spin and orbital order in thin films. It combines first-principles DFT with SPET-based 3D electron diffraction tomography and TEM/XRD to resolve atomic positions and distortion modes across a ~50–53 nm LaVO_3 film grown on a $DyScO_3$ substrate. The study identifies a $[110]$-oriented ground state with $C_{SO}$ order and a near-degenerate $G_{SO}$ state, and provides quantitative mappings of La displacements ($\approx$22.7 pm) and distortion modes ($X_5^-$, $Q_2^+$, $Q_2^-$) alongside octahedral rotations, revealing coherent single-variant epitaxy and thickness-driven evolution toward bulk distortions. Overall, the results yield atomic-scale structure–property data essential for modeling spin–orbital physics in vanadates and demonstrate SPET as a powerful approach for thickness-resolved structure determination in oxide heterostructures.

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.

Nanoscale characterization of atomic positions in orthorhombic perovskite thin films

TL;DR

This work addresses how nanoscale lattice distortions in orthorhombic perovskites influence spin and orbital order in thin films. It combines first-principles DFT with SPET-based 3D electron diffraction tomography and TEM/XRD to resolve atomic positions and distortion modes across a ~50–53 nm LaVO_3 film grown on a substrate. The study identifies a -oriented ground state with order and a near-degenerate state, and provides quantitative mappings of La displacements (22.7 pm) and distortion modes (, , ) alongside octahedral rotations, revealing coherent single-variant epitaxy and thickness-driven evolution toward bulk distortions. Overall, the results yield atomic-scale structure–property data essential for modeling spin–orbital physics in vanadates and demonstrate SPET as a powerful approach for thickness-resolved structure determination in oxide heterostructures.

Abstract

The crystal structure determines many of the physical properties of oxide perovskites (ABO) 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 thin film grown onto (110)-oriented DyScO 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 crystallizes in the orthorhombic space group and is constrained by the substrate, which imposes a growth along the 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, 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.

Paper Structure

This paper contains 4 sections, 3 figures, 3 tables.

Table of Contents

  1. INTRODUCTION
  2. Results and discussion
  3. Conclusion
  4. METHODS

Figures (3)

  • Figure 1: (a) HRTEM cross-section view along the $[\bar{1}10]$ DSO zone axis. EDP of the LVO and DSO region are displayed on the top and bottom of the image, respectively. (b) and (c) sketches of the LVO atomic structure projected along the $[\bar{1}10]$ and $[001]$ directions, respectively. (d) HAADF-STEM observation along the $[\bar{1}10]$ DSO zone axis. (e) mapping of the vertical La-cation displacements from HAADF-STEM image analysis. (f) and (g) mean R-site cation displacement across the growth direction for LVO grown on DSO and STO, respectively. The blue dashed line signals the displacement value in the bulk LVO (34 pm).
  • Figure 2: (a)-(b) Reciprocal space maps around the symmetric (110), (220), (330) and (440) Bragg peaks, respectively. (e)-(h) Reciprocal space maps around the asymmetric (332), (240), (33$\bar{2}$) and (420) Bragg peaks, respectively. (i)-(l) Reciprocal space maps around the (111) Bragg peak, or pseudo-cubic half-order Bragg peak $(\frac{1}{2}01)$, $(0\frac{1}{2}1)$, $(10\frac{1}{2})$ and $(01\frac{1}{2})$, respectively. (110)-oriented LVO displays only the $(\frac{1}{2}01)$ peak. (m)-(o) Reciprocal space maps around the (200), (202) and (204) Bragg peak.
  • Figure 3: (a) STEM-ABF image of the scanned region along the black arrow and the refined area: LVO top, LVO bottom and DSO indicated in white. (b) Schematic representation of the structure of LVO as obtained from PEDT refinements, with the values of the octahedral tilt and rotations.