Charge Transfer Excitation in Resonant X-ray Emission Spectroscopy of NiO

Direct Experimental Probe of the Ni(II)/Ni(III)/Ni(IV) Redox Evolution in LiNi0.5Mn1.5O4 Electrodes

“…These parameters result in a high spin state for Ni 2+ , and low spin states for Ni 3+ and Ni 4+ , and are similar to parameter sets considered in Ref. [17][18] . The LiNi0.5Mn1.5O4 spinel powders used in this study have the typical structural and electrochemical characteristics of standard LNMO spectra reported in literature 19 .…”

“…Implementation details for the model are discussed in Ref. 17 . Slater-Condon parameters were renormalized to 80%, 75% and 70% of Hartree-Fock values for nominal Ni 2+ , Ni 3+ and Ni 4+ calculations, respectively, and the simulation was thermally populated to 300K.…”

Extending resonant inelastic X-ray scattering to the extreme ultraviolet

“…The principle electronic excitations observed in Xray absorption spectroscopy (XAS) and RIXS with p-symmetry core holes on Co [7,16], Ni [6,8,14,15,17,18,36], and Cu [8,9] are closely identified with excitation matrix elements obtained from AM based calculations for a high-spin 2+ valence atomic state perturbed by the crystal field of surrounding oxygen atoms. The compounds CoO and NiO have a rock salt crystal structure, with an octahedral crystal field on the transition metal site, and strong antiferromagnetic superexchange interactions through σ -bonded oxygen atoms.…”

“…Previous experimental studies performed with soft X-rays at the transition metal L-edge (700-900 eV) have noted that charge transfer features from these materials have significant intensity at 4-7 eV energy loss [14,[16][17][18]. M-edge studies have noted that charge transfer excitations are weak, but stopped short of presenting data that covered the Mott gap feature [15,16].…”

“…Second, we focus only on the region within 4 eV of the band gap, as this is where most charge transfer intensity is found at the L-edge, with the exception of the high energy emission line. The emission line is far weaker at the M-edge than at the L-edge, and only low energy parts of the emission line are associated with simple metal-ligand charge transfer in recent models [17,18]. Finally, we assume that the peak intensity of charge transfer excitations is 50% greater than the average intensity of the 4 eV region and, based on the data quality in Figure 3, that a feature with peak intensity greater than 0.01 in several consecutive RIXS curves would be recognizable in the data.…”