Resonant x-ray scattering experiments on electronic orderings in NdNiO3 single crystals

We have carried out resonant x-ray scattering experiments on NdNiO3 single crystals aiming at the observation of a predicted orbital ordering that may explain the presence of an antiferromagnetic ordering with unusual modulation wave vector, q = (1/2, 0, 1/2). A first-order structural phase transition has been observed at T-MI = 200 K although no new superlattice peaks are present at this q position. Our experiment thus rules out the presence of an orbital ordering with this modulation. It rather seems that the magnetic, as well as the electronic, properties of this compound should be explained by introducing models of charge localization, either at the metal sites or at the ligand oxygen. We further comment on the observability of this charge ordering by resonant x-ray scattering.