Thickness-Dependent Perovskite Octahedral Distortions at Heterointerfaces

In this study, we analyze how the octahedral tilts and rotations of thin films of LaNiO₃ and LaAlO₃ grown on different substrates, determined using synchrotron X-ray diffraction-measured half-integer Bragg peaks, depend upon the total film thickness. 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 chemically and structurally discontinuous LaNiO₃/SrTiO₃ and LaAlO₃/SrTiO₃ interfaces cause a large variation in the octahedral network as a function of film thickness whereas the rather continuous LaNiO₃/LaAlO₃ interface seems to allow from just a few unit cells the formation of a stable octahedral pattern corresponding to that expected only given the applied biaxial strain.