The structure of monoclinic NaNiO2 as determined by powder X-ray and neutron scattering

The crystal structure of low temperature NaNiO2 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 NaNiO2 is monoclinic, C2/m, a=0.53192(2), b=0.28451(1), c=0.55826(4) nm, beta-110.449(2)degrees. NaNiO2 has a layered structure. The Ni-O layer is formed by edge sharing of Jahn-Teller elonganted NiO6 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. (C) 1997 International Centre for Diffraction Data.