Oxygen octahedra

Transition metal oxides are really sensitive to subtle structural distortions including distortions that only involve movement of the oxygen ions. In pervoskites, the oxygens are arranged in corner-connected octahedra and one of the most common types of distortion is collective rotations and tilts of the octahedra. Oxygen is the lightest element in these kinds of materials and this makes it hard to see their positions by most methods. We set about trying to do this by synchrotron x-ray diffraction in thin and ultrathin films.

In our 2019 Nano Letters paper we successfully resolved the oxygen positions in films as thin as 2 nm. We saw how the oxygen octahedra evolve as the film thickness increases and saw a strong dependence on the type of substrate selected for the heteroepitaxial thin film.

Using the same approach, in 2020 we showed in our ACS Materials Letters paper that magnitude of octahedral tilting does not change in a film when the substrate undergoes a structural transition. Rather, the domain configuration itself is what changes and this leads to highly anisotropic transport properties in the lower symmetry phase.