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

Abstract

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, β=110.449(2)°. 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 Rwp=0.069, RI=0.059, Rexp=0.059 for the neutron and Rwp=0.032, RI=0.034, Rexp=0.017 for the X-ray data.