Intra- versus inter-site electronic excitations in NdNiO3 by resonant inelastic ultra-soft X-ray scattering at Ni 3p edge

Resonant ultra-soft X-ray scattering measurements performed on NiO, as a model system, and NdNiO3 reveal the presence of pronounced inelastic structures within a few eV below the elastic peak in both cases. A comparison of experimental data with the results of Anderson impurity model calculations indicates that for both oxides the inelastic part of recorded spectra mainly originates from the intra-atomic d–d excitations. Remarkably, no distinct signal from inter-site d–d transitions can be identified for both metallic and insulating NdNiO3 at small energy-losses. The lack of significant spectral contribution from the latter transitions in this compound indicates that states on the top (bottom) of the valence (conduction) band have predominantly O 2p character and the NdNiO3 insulator is rather of a p–p type.