Open accessJournal Article

# Orientation-dependent x-ray Raman scattering from cubic crystals: Natural linear dichroism in MnO and CeO2

01 Nov 2009-Vol. 190, Iss: 1, pp 012047
Abstract: Information on valence orbitals and electronic interactions in single crystal systems can be obtained through orientation-dependent x-ray measurements, but this can be problematic for a cubic system. Polarisation-dependent x-ray absorption measurements are common, but are dominated by dipole transitions which, for a cubic system, are isotropic even though a cubic system is not. Many edges, particularly for transition metals, do have electric quadrupole features that could lead to dichroism but proximity to the dipole transition can make interpretation challenging. X-ray Raman Spectroscopy (XRS) can also be used to perform orientation-dependent near-edge measurements - not only dependent on the direction of the momentum transfer but also its magnitude, q. Previous XRS measurements on polycrystalline materials revealed that multipole (higher order than dipole) transitions are readily observable in the pre-threshold region of rare earth N4,5 edges, actually replacing the dipole at high-q. We have extended these studies to examine orientation-dependent XRS for CeO2 and MnO single crystals, as prototype systems for theoretical treatment. Dichroism is observed at both the Ce N4,5 and Mn M2,3 edges in these cubic materials.

Topics: Dipole (57%), Linear dichroism (54%),  ...read more
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Open accessJournal Article
09 Apr 2012-Physical Review B
Abstract: We demonstrate how ab initio cluster calculations including the full Coulomb vertex can be done in the basis of the localized Wannier orbitals which describe the low-energy density functional (local-density approximation) band structure of an infinite crystal, e.g., the transition-metal $3d$ and oxygen $2p$ orbitals. The spatial extent of our $3d$ Wannier orbitals (orthonormalized $N$th-order muffin-tin orbitals) is close to that found for atomic Hartree-Fock orbitals. We define ligand orbitals as those linear combinations of the O $2p$ Wannier orbitals which couple to the $3d$ orbitals for the chosen cluster. The use of ligand orbitals allows for a minimal Hilbert space in multiplet ligand-field theory calculations, thus reducing the computational costs substantially. The result is a fast and simple ab initio theory, which can provide useful information about local properties of correlated insulators. We compare results for NiO, MnO, and SrTiO${}_{3}$ with x-ray absorption, inelastic x-ray scattering, and photoemission experiments. The multiplet ligand-field theory parameters found by our ab initio method agree within $\ensuremath{\sim}10%$ with known experimental values.

Topics: , Basis set (71%),  ...read more

232 Citations

Open accessJournal Article
Simo Huotari1, Ch. J. Sahle, Ch. Henriquet, Ali Al-Zein2  +9 moreInstitutions (3)
Abstract: An end-station for X-ray Raman scattering spectroscopy at beamline ID20 of the European Synchrotron Radiation Facility is described. This end-station is dedicated to the study of shallow core electronic excitations using non-resonant inelastic X-ray scattering. The spectrometer has 72 spherically bent analyzer crystals arranged in six modular groups of 12 analyzer crystals each for a combined maximum flexibility and large solid angle of detection. Each of the six analyzer modules houses one pixelated area detector allowing for X-ray Raman scattering based imaging and efficient separation of the desired signal from the sample and spurious scattering from the often used complicated sample environments. This new end-station provides an unprecedented instrument for X-ray Raman scattering, which is a spectroscopic tool of great interest for the study of low-energy X-ray absorption spectra in materials under in situ conditions, such as in operando batteries and fuel cells, in situ catalytic reactions, and extreme pressure and temperature conditions.

Topics: , High-energy X-rays (63%), Scattering (61%) ...read more

57 Citations

Open accessJournal Article
Maurits W. Haverkort1Institutions (1)
01 Dec 2016-
Abstract: Depending on the material and edge under consideration, core level spectra manifest themselves as local excitons with multiplets, edge singularities, resonances, or the local projected density of states. Both extremes, i.e., local excitons and non-interacting delocalized excitations are theoretically well under control. Describing the intermediate regime, where local many body interactions and band-formation are equally important is a challenge. Here we discuss how Quanty, a versatile quantum many body script language, can be used to calculate a variety of different core level spectroscopy types on solids and molecules, both in the frequency as well as the time domain. The flexible nature of Quanty allows one to choose different approximations for different edges and materials. For example, using a newly developed method merging ideas from density renormalization group and quantum chemistry [1-3], Quanty can calculate excitons, resonances and band-excitations in x-ray absorption, photoemission, x-ray emission, fluorescence yield, non-resonant inelastic x-ray scattering, resonant inelastic x-ray scattering and many more spectroscopy types. Quanty can be obtained from: http://www.quanty.org.

Topics: , Density of states (55%), Spectroscopy (52%) ...read more

54 Citations

Open accessJournal Article
Martin Sundermann1, Hasan Yavaş, Kai Chen2, Dae-Jeong Kim3  +6 moreInstitutions (4)
Abstract: We investigated the crystal-electric field ground state of the $4f$ manifold in the strongly correlated topological insulator ${\mathrm{SmB}}_{6}$ using core-level nonresonant inelastic x-ray scattering. The directional dependence of the scattering function that arises from higher multipole transitions establishes unambiguously that the ${\mathrm{\ensuremath{\Gamma}}}_{8}$ quartet state of the Sm ${f}^{5}\text{ }\text{ }J=5/2$ configuration governs the ground-state symmetry and, hence, the topological properties of ${\mathrm{SmB}}_{6}$. Our findings contradict the results of density functional calculations reported so far.

42 Citations

Journal Article
Christian Sternemann1, Max Wilke2Institutions (2)
Abstract: X-ray Raman scattering spectroscopy is an emerging method in the study of low and intermediate Z elements' core-electron excitations at extreme conditions in order to reveal information on local structure and electronic state of matter in situ. We discuss the capabilities of this method to address questions in Earth materials' science and demonstrate its sensitivity to detect changes in the oxidation state, electronic structure, coordination, and spin state. Examples are presented for the study of the oxygen K-, silicon L- and iron M-edges. We assess the application of both temperature and pressure in such investigations exploiting diamond anvil cells in combination with resistive or laser heating which is required to achieve realistic conditions of the Earth's crust, mantle, and core.

Topics: , Diamond anvil cell (56%), Spectroscopy (53%) ...read more

29 Citations

##### References
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Journal Article
01 Jul 1998-Surface Science
Abstract: Valence band photoemission (XPS), valence band electron energy loss spectroscopy (EELS), Ce 3d and 4d XPS, O 1s XPS and O 1s X-ray absorption (XAS) have been investigated for oxidized and sputtered single crystal CeO 2 films and for oxidized Ce foil. Features were identified that distinguish between the Ce 4+ or Ce 3+ oxidation states. Ce 4+ was identified by the highest binding energy peaks in the Ce 4d spectrum at 122.8 eV and 126.0 eV and lowest energy peak in the O 1s XAS spectrum at 530 eV. Ce 3+ was identified by the lowest binding energy peak in the Ce 4d spectrum at 105.4 eV, the Ce 4f valence level peak at 2.0 eV and excitations in the band gap in EELS. The Ce 4d spectra are similar to the Ce 3d spectra in that satellite peaks that are related to the final state occupation of the Ce 4f level dominate the spectra. The interpretation of the Ce 4d spectra is more complicated than that of the Ce 3d spectra, however, due to multiplet splitting which has a greater influence in the Ce 4d spectra. The O 1s XAS are much easier to interpret than XAS spectra from the Ce core levels. The O 1s XAS spectra reflect the unoccupied density of states of the cerium oxide without being significantly affected by final state relaxation of the Ce energy levels. The O 1s XPS spectra show only a 0.3 eV difference in binding energy between Ce 4+ and Ce 3+ in the oxides provided the spectra are corrected for band bending.

Topics: Band gap (56%), , Binding energy (55%) ...read more

785 Citations

Open accessJournal Article
11 Jan 2007-Physical Review B
Abstract: The electronic structure and properties of cerium oxides ($\mathrm{Ce}{\mathrm{O}}_{2}$ and ${\mathrm{Ce}}_{2}{\mathrm{O}}_{3}$) have been studied in the framework of the $\mathrm{LDA}+\mathrm{U}$ and $\mathrm{GGA}(\mathrm{PW}91)+\mathrm{U}$ implementations of density functional theory. The dependence of selected observables of these materials on the effective U parameter has been investigated in detail. The examined properties include lattice constants, bulk moduli, density of states, and formation energies of $\mathrm{Ce}{\mathrm{O}}_{2}$ and ${\mathrm{Ce}}_{2}{\mathrm{O}}_{3}$. For $\mathrm{Ce}{\mathrm{O}}_{2}$, the $\mathrm{LDA}+\mathrm{U}$ results are in better agreement with experiment than the $\mathrm{GGA}+\mathrm{U}$ results whereas for the computationally more demanding ${\mathrm{Ce}}_{2}{\mathrm{O}}_{3}$ both approaches give comparable accuracy. Furthermore, as expected, ${\mathrm{Ce}}_{2}{\mathrm{O}}_{3}$ is much more sensitive to the choice of the U value. Generally, the PW91 functional provides an optimal agreement with experiment at lower U energies than LDA does. In order to achieve a balanced description of both kinds of materials, and also of nonstoichiometric $\mathrm{Ce}{\mathrm{O}}_{2\ensuremath{-}x}$ phases, an appropriate choice of U is suggested for $\mathrm{LDA}+\mathrm{U}$ and $\mathrm{GGA}+\mathrm{U}$ schemes. Nevertheless, an optimum value appears to be property dependent, especially for ${\mathrm{Ce}}_{2}{\mathrm{O}}_{3}$. Optimum U values are found to be, in general, larger than values determined previously in a self-consistent way.

Topics: Order (ring theory) (61%)

555 Citations

Journal Article
N. V. Skorodumova1, Rajeev Ahuja2, S. I. Simak1, Igor A. Abrikosov2  +3 moreInstitutions (3)
28 Aug 2001-Physical Review B
Abstract: First-principles electronic structure calculations of cerium oxide in two forms, ${\mathrm{CeO}}_{2}$ and ${\mathrm{Ce}}_{2}{\mathrm{O}}_{3},$ are presented. The $4f$ state of Ce is treated as a part of the inner core in ${\mathrm{Ce}}_{2}{\mathrm{O}}_{3}$ and as a valence-band-like state in ${\mathrm{CeO}}_{2}.$ The calculated ground-state and magnetic properties of the Ce (III) oxide are shown to be in agreement with available experimental data as well as the calculated ground-state and optical properties of Ce (IV) dioxide. The nature of the bonding in cerium oxide is discussed on the basis of an analysis of the charge-density and electron localization function distributions and described as a polarized ionic bond in both oxides.

295 Citations

Open accessJournal Article
01 Jan 2001-Physical Review B
Abstract: First-principles electronic structure calculations of cerium oxide in two forms, CeO2 and Ce2O3, are Presented. The 4f state of Ce is treated as a part of the inner core in Ce2O3 and as a valence-band-like state in CeO2,. The calculated ground-state and m

Topics: Cerium oxide (60%), Electronic structure (54%), Inner core (51%)

267 Citations

Journal Article
S. L. Altmann1, A. P. Cracknell1Institutions (1)
Abstract: A review is given of some conventions and definitions required for the derivation of the irreducible representations of the space groups, and of a method to obtain lattice harmonics. These are given for all the irreducible representations of the simple cubic ($\mathrm{Pm}3m$), face-centered cubic ($\mathrm{Fm}3m$) and body-centered cubic ($\mathrm{Im}3m$) space groups for $l\ensuremath{\le}12$. The expansions are given in polar coordinates and care has been taken that different bases corresponding to the same representation span identical, rather than equivalent, representations, which are given in full. Moreover, all the different expansions listed in the tables are fully orthogonal.

Topics: , Cubic form (60%), Tschirnhausen cubic (52%) ...read more

181 Citations

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