A neutron diffraction study of structural distortions in the Ruddlesden-Popperphase Na2La2Ti3O10

The structure of Na2La2Ti3O10 (tetragonal, space group I4/mmm) has been re-examined using time-of-flight powder neutron diffraction in order to clarify uncertainties remaining from an X-ray diffraction study. One of the oxygen atoms is shown to be displaced significantly from its ideal position, the shift being consistent with the rotation of one of the TiO6 octahedra by ca. 12.5 degrees around the [001] direction. This rotation allows fora 2.5% increase in four of the Ti-O bond lengths and a corresponding decrease in the bond valence sum from 4.9 to 4.1. The structural distortion is similar to that observed previously at overbonded octahedral sites in related structures.