Evidence of Paracrystalline Cation Order in the Ruddlesden–Popper Phase LaSr3NiRuO8 through Neutron Total Scattering Techniques

Cation ordering in perovskite-derived phases can lead to a wealth of tunable physical properties. Ordering is typically driven by a large difference between the cation size and charge, but many Ruddlesden–Popper phases An+1BnO3n+1 appear to lack such B-site ordering, even when these differences are present. One such example is the “double” Ruddlesden–Popper n = 1 composition LaSr3NiRuO8. In this material, a lack of B-site ordering is observed through traditional crystallographic techniques, but antiferromagnetic ordering in the magnetism data suggests that B-site cation ordering is indeed present. Neutron total scattering, particularly analysis of the neutron pair distribution function, reveals that the structure is locally B-site-ordered below 6 A but becomes slightly disordered in the midrange structure around 12 A. This provides evidence for paracrystalline order in this material: cation ordering within a single perovskite sheet that lacks perfect registry within the three-dimensional stack of sheets. ...