Hole distribution between the Ni3dand O2porbitals inNd2−x

Abstract

General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. We present a joint experimental and theoretical study of x-ray absorption at the O-K and Ni-L 2,3 thresholds of Nd 2Ϫx Sr x NiO 4Ϫ␦ providing an analysis of the distribution of doped holes induced by Sr substitution between Ni 3d and O 2p orbitals. The preedge peak in the O-K x-ray absorption ͑XAS͒ spectra, reflecting holes located in the O 2p orbitals, increases monotonically with the degree of Sr doping up to the maximum doping level studied (xϭ1.4). The saturation in the relative intensity of the O-K preedge peak in the analogous lanthanum nickelate reported in the literature is shown to be most likely due to surface oxygen deficiency. Furthermore, the experimental Ni-L 2,3 XAS spectrum of the Ni͑III͒ nickelate Nd 1.1 Sr 0.9 NiO 3.95 was simulated by a cluster approach, including charge-transfer and complete multiplet interactions, and compared with the corresponding spectrum of the Ni͑III͒ system Nd 2 Li 0.5 Ni 0.5 O 4 . The 3d 7 weight in the ground state of Nd 1.1 Sr 0.9 NiO 3.95 was found to be 42%, somewhat smaller than the value of 51% found for Nd 2 Li 0.5 Ni 0.5 O 4 . This indicates the influence of nonlocal effects in x-ray-absorption spectroscopy, which, in this case is due to the increased covalency in the Sr-doped system as a result of inter-NiO 6 -cluster interaction. Such interactions are absent in Nd 2 Li 0.5 Ni 0.5 O 4 , which is characterized by having isolated NiO 6 clusters.

Surface reconstruction and chemical evolution of stoichiometric layered cathode materials for lithium-ion batteries

“…The corresponding transition metal L-edge spectra exhibit no variation in the shapes or L3/L2 ratios at different probing positions. Furthermore, the O K-edge shows identical pre-edge peaks that are associated with the transitions from O 1s to O 2p-metal 3d hybridized states and are sensitive to the oxidation states of transition metals 38,39 , which implies that the average oxidation states of transition metals remain constant from the top surfaces to volumes deep in the bulk. The above ensemble-averaged and spatially resolved spectroscopic studies allow us to conclude that the pristine NMC material exhibits a well-defined R 3m crystal structure with a homogenous distribution of the electronic structure.…”

The electronic structure of the doped one-dimensional transition metal oxide Y 2 - x Ca x BaNiO 5 studied using X-ray absorption

“…It was found previously that the covalence was decreased (the 3d 7 weight was increased) by nearly 10% going from compounds with interconnected to systems with isolated NiO 6 clusters [31]. In addition, this delocalization of the electronic states along the chains offers the system a further opportunity to screen the Ni 2p core hole via ligand electrons in such a core level spectroscopy.…”

Electronic structure of titania-based nanotubes investigated by EELS spectroscopy

“…Details of the calculation techniques can be found in references. 13,[28][29][30][31] The difference U dd − U pd is important since it relates to the charge-transfer energy in the final state ⌬ f = E͑c គd n+1 L គ ͒ − E͑c គd n ͒, where c គ denotes the Ti 2p core hole, through the estimation ⌬ f = ⌬ i − ͑U pd − U dd ͒. 28 The intensity of the charge-transfer excitations with respect to the main peak are indeed related to the difference in energy between ⌬ i and ⌬ f ͑for ⌬ i = ⌬ f , no satellite peaks should be observed in the EELS spectrum 13 ͒.…”