The structure of monoclinic NaNiO 2 as determined by powder X-ray and neutron scattering

The crystal structure of low temperature NaNiO 2 has been refined by Rietveld methods using powder X-ray diffraction and neutron scattering data. The starting model was based on parameters that had been obtained earlier by X-ray film methods. At room temperature NaNiO 2 is monoclinic, C 2/ m , a =0.53192(2), b =0.28451(1), c =0.55826(4) nm, β=110.449(2)°. NaNiO 2 has a layered structure. The Ni–O layer is formed by edge sharing of Jahn–Teller elonganted NiO 6 octahedra with Ni–O distances of 0.1911(2) nm and 0.2144(4) nm. The Na ions between these layers also exhibit a distorted octahedral coordination with Na–O distances of 0.2328(2) nm and 0.2369(4) nm. The final R values were R wp =0.069, R I =0.059, R exp =0.059 for the neutron and R wp =0.032, R I =0.034, R exp =0.017 for the X-ray data.