Neutron Diffraction Study of the Structural Distortions in Sr3Ru2O7

It is shown that due to the ionic sizes of Sr2+ and Ru4+, crystal structure distortions are expected in the layered structure of Sr3Ru2O7. Using neutron powder diffraction of Sr3Ru2O7, the expected distortions are indeed found and their nature is studied at room temperature. It is found that among the eight possible modes of pure rotations (i.e., rotations along symmetry axes) of the oxygen octahedra, only one mode is consistent with the neutron data. In this mode the octahedra rotate about the c axis with intra- and interbilayer order. This ordered model is in contrast to a previously reported semi-ordered model, where the rotations in every other bilayer have interbilayer disorder.