Quantifying octahedral rotations in strained perovskite oxide films

We have measured the oxygen positions in ${\text{LaNiO}}_3$ films to elucidate the coupling between epitaxial strain and oxygen octahedral rotations. The oxygen positions are determined by comparing the measured and calculated intensities of half-order Bragg peaks, arising from the octahedral rotations. Combining ab initio density-functional calculations with these experimental results, we show how strain systematically modifies both bond angles and lengths in this functional perovskite oxide.