Quantifying octahedral rotations in strained perovskite oxide films S. J. May, 1, 2, ∗ J.-W. Kim, 3 J. M. Rondinelli, 4 E. Karapetrova, 3 N. A. Spaldin, 4 A. Bhattacharya, 1, 5 and P. J. Ryan 3 1 Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA 2 Department of Materials Science and Engineering, Drexel University, Philadelphia, PA 19104, USA 3 Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA 4 Materials Department, University of California, Santa Barbara, CA 93106, USA 5 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL 60439, USA (Dated: October 22, 2018) Epitaxial strain is a proven route to enhancing the properties of complex oxides, however, the details of how the atomic structure accommodates strain are poorly understood due to the difficulty of measuring the oxygen positions in thin films. We present a general methodology for determining the atomic structure of strained oxide films via x-ray diffraction, which we demonstrate using LaNiO$_{3}$ films. The oxygen octahedral rotations and distortions have been quantified by comparing the intensities of half-order Bragg peaks, arising from the two unit cell periodicity of the octahedral rotations, with the calculated structure factor. Combining ab initio density functional calculations with these experimental results, we determine systematically how strain modifies the atomic structure of this functional oxide. Abstract arXiv:1002.1317v1 [cond-mat.mtrl-sci] 5 Feb 2010 1