Experimental and Theoretical Studies of Fine Structure in Polarized Ni K X-Ray Absorption Spectra of NiO Single Crystals

Abstract

Polarized Ni K XANES of single crystal NiO is studied experimentally and theoretically for two crystal orientations relative to the polarization and wave vectors of incident X-ray beam. The spectra calculated by the full multiple scattering method for a spin-dependent cluster potential and incomplete screening of the core hole appear to be in an excellent agreement with the experiment. The low energy pre-edge peak is shown to be caused by the quadrupole transitions of the Ni 1s electron to an exciton-type state shifted down by $4 eV from the empty e g high-energy conduction band under the influence of the core hole potential. The feature caused by the Ni 1s ! e g band dipole transitions is also recognized in the spectrum. It is shown that the same mechanisms, which are responsible for the formation of the pre-edge fine structure in the oxides of early 3d-metals in 3d 0 state, work in the considered case as well. A comparative analysis outlining the significance of different mechanisms for the pre-edge structure formation in cases of early and late 3d-metal spectra is presented. The antiferromagnetic order of the absorber is taken into account within oneelectron approximation.Die polarisierte Ni K XANES von einkristallinem NiO wurde experimentell und theoretisch fü r zwei Kristallorientierungen relativ zum Polarisations-und Wellenvektor des einfallenden Rö ntgenstrahls untersucht. Die Spektren wurden nach der Full-multiple-scattering Methode fü r ein spinabhä ngiges Clusterpotential und fü r unvollstä ndige Abschirmung des Rumpfloches in exzellenter Ûbereinstimmung mit dem Experiment berechnet. Die niederenergetische Vorkantenabsorption wird durch Quadrupolü bergä nge von Ni 1s Elektronen in einen exzitonä hnlichen Zustand erklä rt, der durch das Rumpflochpotential um $4 eV gegenü ber dem unbesetzten e gartigen Leitungsband abgesenkt ist. Die aus den Ni 1s ! e g Dipolü bergä ngen berechneten Strukturen sind auch in den experimentellen Spektren zu erkennen. Es wird gezeigt, da im vorliegenden Fall die gleichen Mechanismen wirken, die auch fü r das Auftreten der Vorkantenabsorption bei den frü hen 3d-Metalloxiden im 3d 0 -Zustand verantwortlich sind. Eine vergleichende Analyse der Bedeutung der verschiedenen Mechanismen fü r das Entstehen der Vorkantenstruktur bei den Verbindungen der 3d-Metalle niedriger und hö herer Ordnungszahl wird durchgefü hrt.

Interpretation of the Ni K-edge EXAFS in nanocrystalline nickel oxide using molecular dynamics simulations

“…1) was assigned to the quadrupole 1s→3d transition from the analysis of resonant x-ray magnetic scattering in [27]. Its quadrupole origin was also supported by several theoretical calculations [29,31,32].…”

“…The preedge region of the XANES provides with the information on the local electronic structure at the absorbing Ni atoms in the presence of the core-hole. In particular, the Ni K-edge absorption is caused by the transition of a 1s electron of nickel from its The interpretation of the Ni K-edge XANES in NiO has been a topic of extensive studies in the past [26,27,28,29,30,31,32,33]. The use of the multiple-scattering approach allowed understanding the origin of main peaks to be due to the scattering by atoms of the first ten coordination shells surrounding the absorber [26,30].…”

XAFS studies of the short-range order in Ni nanoparticles embedded in carbonacoues matrix

“…They are widely described features of transition metal absorption spectra (e.g. [7][8][9][10][11]). The Ni K edge position in the energy scale was chosen as the coordinate of the first inflection point associated with the pre-edge bump.…”

Resonant diffraction inFeS2:Determination of the x-ray polarization anisotropy of iron atoms

“…The latter is constructed in the same way as in earlier successful XANES calculations. [52][53][54][55] Accordingly the atomic electron densities are calculated by the Herman-Skillman code 56 which employs a spin-independent local X␣ potential and the ␣ parameter determined by Schwarz. 57 The electron configurations of the nonresonant scattering atoms are considered to be those of free atoms.…”