Thickness-dependent oxygen octahedral distortions in perovskite thin films as an adaption to the heterointerface

Distortions of the oxygen octahedral network of ABO₃-type perovskites are one of the most common features that develop in oxide heterostructures as a response to the epitaxial strain imposed by the substrate. This behaviour, which can be characterised as rigid tilts and rotations of the octahedra themselves, is readily studied quantitatively by synchrotron x-ray diffraction at half-integer Bragg positions [1].

In this study, we analyse the thickness-dependence of the octahedral tilts and rotations of thin films of LaNiO₃. We find a striking difference between films grown on SrTiO₃ and LaAlO₃ substrates, which appears to stem not only from the difference in epitaxial strain state but also from the level of continuity at the heterointerface. In particular, the highly discontinuous LaNiO₃/SrTiO₃ interface causes a large variation in the octahedral network as a function of film thickness whereas the rather continuous LaNiO₃/LaAlO₃ interface seems to allow the immediate formation of a stable octahedral pattern corresponding to simply the applied biaxial strain from just a few unit cells.

The scope for structural engineering by exploitation of these interfacial effects is tangible.

[1]. S. J. May et al, Phys. Rev. B 82, 014110 (2010)