OXYGEN DEFECT STRUCTURE IN LA2NIO4+DELTA

The structure of La2NiO4.13 has been studied as a function of temperat ure (20-673 K) with single crystal neutron diffraction. In order to ac hieve a high resolution, data sets were measured up to 1.05 Angstrom(- 1). Structure refinements were carried out in the space group F4/mmm. Due to the incorporated oxygen on interstitial lattice sites the apica l oxygen becomes disordered and the NiO6 octahedra are partly tilted a round the [110] direction. The disorder is still present at temperatur es above the high temperature orthorhombic/tetragonal phase transition of stoichiometric La2NiO4.00 at 670 K.