Study of perovskite heterostructures shows how crystal geometry intricately responds to strain

Transition metal-based perovskite structures have shown immense promise as versatile insulators, superconductors and ferromagnets. One area of interest has been in layering orthorhombic thin films with different cations to produce heterostructures with both ferromagnetic and ferroelectric properties. Publishing its work in APL Materials, a researcher team has taken the first step toward assembling these highly versatile materials by characterizing the structure of vanadate thin films.

The group provided a detailed analysis of epitaxial constraint effects on lanthanum vanadate (LaVO₃) thin films. Using X-ray diffraction and scanning transmission electron microscopes, they characterized changes in the crystal geometry of different layers when the thin films were grown on different substrates that provided compressive and tensile biaxial strain.

The authors found that at the interface between the LaVO₃ film and the substrate, LaVO₃’s orthorhombic configuration lets the material adjust to the substrate’s epitaxial strain by assuming different oxygen rotational patterns. The different tilt patterns assumed to minimize the strain lead to different crystal orientations in space. Calculations using density functional theory also supported their results.

Temperature-dependent X-ray diffraction revealed distortions in the structure of the LaVO₃ films, which the paper suggests occur because the strain affects the orbital order of the films’ ground states. As the temperature evolved, there was no change in the out-of-plane lattice parameter in thin films grown under compressive strain on strontium titanate, whereas the film grown under tensile strain, on dysprosium scandate, exhibited an out-of-plane lattice parameter that transitioned upward with temperature.

Next the team plans to couple LaVO₃ crystals to other perovskite crystals to one day produce heterostructures that demonstrate both ferromagnetic and ferroelectric properties.

Source: “Structural analysis of LaVO₃ thin films under epitaxial strain,” by H. Meley, Karandeep, L. Oberson, J. de Bruijckere, D. T. L. Alexander, J.-M. Triscone, Ph. Ghosez, and S. Gariglic, APL Materials (2018). The article can be accessed at https://doi.org/10.1063/1.5021844 .