Résumé
In this work, we present a study of the CEF environment in Pr 2 NiO 4+δ (δ = 0.25), through the analysis of inelastic neutron scattering measurements combined with point charge model simulations. Inelastic neutron scattering experiments on Pr 2 NiO 4.25 were conducted using the thermal triple-axis spectrometer IN20 at the Institut Laue-Langevin. An inelastic peak was observed at 5.58 meV, which shifted to 6.30 meV upon lowering the temperature to 1.5 K. At 300 K, no peak was observed within this energy transition range. Using point charge model calculations, we analysed the crystal electric field effects on the energy levels of the Pr 3+ magnetic ions. The CEF calculations, performed with the PyCrystalField program, provided an approximate understanding of the CEF environment of the over-stoichiometric Pr 2 NiO 4.25 . The calculations showed that the strong peak seen at low temperatures in inelastic neutron scattering experiments comes from two singlets corresponding to the first energy levels of the Pr 3+ sites without interstitial oxygen. While the first transition for the Pr 3+ with interstitial as ligand shows an energy much lower, close to the elastic line that barely we could resolve in our scans. Moreover, the calculations revealed a strong link between the position of the first energy transition peak and the Pr-O ap atomic distances.