A5060272326- X-ray Spectroscopy and Fluorescence Analysis
- X-ray Diffraction in Crystallography
- High-pressure geophysics and materials
- Glass properties and applications
- Crystallography and Radiation Phenomena
- Electron and X-Ray Spectroscopy Techniques
- Luminescence Properties of Advanced Materials
- Crystal Structures and Properties
- Nuclear materials and radiation effects
- Electromagnetic Scattering and Analysis
- Advanced Condensed Matter Physics
- Magnetism in coordination complexes
- Mineralogy and Gemology Studies
- Pigment Synthesis and Properties
- Iron oxide chemistry and applications
- Geological and Geochemical Analysis
- Inorganic Fluorides and Related Compounds
- Advanced NMR Techniques and Applications
- Clay minerals and soil interactions
- History and advancements in chemistry
- Molecular spectroscopy and chirality
- Solid-state spectroscopy and crystallography
- Magnetic Properties and Synthesis of Ferrites
- Optical Coatings and Gratings
- Atomic and Molecular Physics
Institut de minéralogie, de physique des matériaux et de cosmochimie
2014-2024
Centre National de la Recherche Scientifique
2013-2022
Sorbonne Université
2013-2022
Laboratoire de Cristallographie et RMN Biologiques
1996-2022
Sorbonne Paris Cité
2022
Institut de Recherche pour le Développement
2009-2021
John Wiley & Sons (United States)
2019
Charles River Laboratories (Netherlands)
2019
Délégation Ile-de-France Villejuif
2017-2018
UPMC Health System
2017
We present a reciprocal-space pseudopotential scheme for calculating x-ray absorption near-edge structure (XANES) spectra. The incorporates recursive method to compute cross section as continued fraction. fraction formulation of is advantageous in that it permits the treatment core-hole interaction through large supercells (hundreds atoms). compared with recently developed Bethe-Salpeter approach. applied carbon K edge diamond and silicon oxygen edges $\ensuremath{\alpha}$-quartz which...
We first present an extended introduction of the various methods used to extract electronic and structural information from K pre-edge X-ray absorption spectra 3d transition metal ions. The structure is then modelled for a selection compounds analyzed using first-principles calculations based on density functional theory (DFT) in local approximation (LDA). selected under study are presented ascending order complexity, starting with Ti K-edge rutile anatase, finishing Fe cyanomet-myoglobin....
We present the first successful attempt at calculating cluster full-potential x-ray absorption near-edge structure (XANES) spectra, based on finite difference method. By fitting XANES simulations onto experimental spectra we are able to perform electron population analysis. The method is tested in case of Ti $K$-edge spectrum ${\mathrm{TiO}}_{2}$, where amount charge transfer between and O atoms screening photoabsorber obtained taking into account both dipolar quadrupolar transitions.
Theoretical predictions show that depending on the populations of Fe 3d xy , xz and yz orbitals two possible quintet states can exist for high-spin state photoswitchable model system [Fe(terpy)2]2+. The differences in structure molecular properties these 5B2 5E quintets are very small pose a substantial challenge experiments to resolve them. Yet better understanding physics this system, which lead design novel molecules with enhanced photoswitching performance, it is vital determine reached...
The pre-edge region of Ti N-edge polarized XANES spectra in TiO2-mtile is investigated by full-potential calculations based on the finite-difference method.Both dipolar and quadrupolar transitions are considered.The use of"non muffin-tin" potential allows a clear interpretation features.The results consistent with Full-potential LAPW band structure calculations, also compared multiple-scattering calculations.
We report the first experimental detection of x-ray magnetochiral dichroism in magnetoelectric ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$. This dichroism, which does not require any polarized beam, is related to time-reversal odd part optical activity tensor dominated by electric dipole-electric quadrupole $E1E2$ interference terms. The experiments were carried out using either a single crystal or powdered pellet required grow antiferromagnetic domain annealing. new element (edge) specific...
We present full multiple-scattering calculations at the aluminium K edge that we compare with experiments for four crystalline silicates and oxide minerals. In different minerals atoms are either fourfold or sixfold coordinated to oxygen in Al sites poorly symmetric. The based on choices of one-electron potentials according coordinations crystallographic structures compounds. Hence it is possible determine how near-edge spectral features a sensitive probe effective potential seen by...
The angular dependence (x-ray linear dichroism) of the $\text{Cr}\text{ }K$ pre-edge in ${\text{MgAl}}_{2}{\text{O}}_{4}:{\text{Cr}}^{3+}$ spinel is measured by means x-ray absorption near-edge structure spectroscopy and compared to calculations based on density functional theory (DFT) ligand field multiplet (LFM) theory. We also present an efficient method, symmetry considerations, compute dichroism cubic crystal starting from a single substitutional site. DFT shows that electric dipole...
The influence of atomic vibrations on x-ray absorption near edge structure (XANES) is calculated by assuming that vibrational energies are small with respect to the instrumental resolution. resulting expression shows that, at K-edge, enable electric dipole transitions 3s and 3d final states. theory applied K-edge Al in Al2O3 corundum Ti TiO2 rutile compared experiment. At sizeable towards states obtained, leading a clear improvement agreement experimental spectra. explain temperature...
The structural environment of a substitutional ${\mathrm{Cr}}^{3+}$ ion in $\mathrm{Mg}{\mathrm{Al}}_{2}{\mathrm{O}}_{4}$ spinel has been investigated by Cr $K$-edge extended x-ray absorption fine structure and near edge (XANES) spectroscopies. First-principles computations the relaxation XANES spectrum have performed, with good agreement experiment. Cr-O distance is close to that $\mathrm{Mg}{\mathrm{Cr}}_{2}{\mathrm{O}}_{4}$, indicating full first neighbors, second shell Al atoms relaxes...
We determine the local crystallographic and electronic structure around chromium impurity in emerald (a doped beryl) by combining ab initio density functional calculations x-ray absorption experiments both near edge (XANES) extended fine (EXAFS) regions. The isotropic natural linear dichroic signals at Cr $K$ have been recorded using single crystals a reliable method has applied to remove diffraction peaks. contributions of electric dipolar quadrupolar transitions XANES preedge are...
O $K$-edge x-ray absorption near-edge structure (XANES) spectra of $\ensuremath{\alpha}$-quartz-type and rutile-type $\mathrm{Ge}{\mathrm{O}}_{2}$ polymorphs ${\mathrm{K}}_{2}{\mathrm{Ge}}_{8}{\mathrm{O}}_{17}$ have been analyzed using first-principles plane-wave pseudopotential calculations. XANES calculated supercell including core-hole effects good agreement with experiment has obtained. In the case polymorphs, local density empty states performed peaks in experimental can be assigned to...
In material sciences, spectroscopic approaches combining ab initio calculations with experiments are commonly used to accurately analyze the experimental spectral data. Most state-of-the-art first-principles usually performed assuming an equilibrium static lattice. Yet, nuclear motion affects spectra even when reduced zero-point at 0 K. We propose a framework based on density-functional theory that includes quantum thermal fluctuations in theoretical x-ray absorption near-edge structure...
We determine the structural relaxations around paramagnetic impurities (Ti, Cr, Fe) in corundum (alpha-Al2O3), by combining x-ray absorption near edge structure (XANES) experiments and ab initio calculations. The are found to be very local. then show that XANES is sensitive small variations interatomic distances within coordination shell of absorbing atom. were carried out on single crystals ruby sapphires. Linear dichroic signals essential characterize geometry impurity site. calculations...
Abstract New results on the local chemical environment of Cu 2+ in archaeological Egyptian blue and green also modern were obtained by x‐ray absorption fine structure (XAFS) analysis. The information is essential for understanding colouring mechanisms both pigments. In a previous study, clear physico‐chemical characterisation was achieved using complementary analytical approach with ancient synthesized Electron microscopy (SEM–EDX TEM), diffraction micro‐Raman UV–visible spectroscopy used to...
Probing the local environment of low-Z elements, such as oxygen, is great interest for understanding atomic-scale behavior in materials, but it requires experimental techniques allowing to work with versatile sample environments. In this paper, lithium borate crystals investigated using non-resonant inelastic X-ray scattering (NRIXS) at energy losses corresponding oxygen K-edge. Large variations spectral features are observed close edge onset 535–540 eV range when varying Li2O content....
Recent experiments have demonstrated the existence of previously unknown iron oxides at high pressure and temperature including newly discovered pyrite-type FeO2 FeO2Hx phases stable deep terrestrial lower mantle pressures temperatures. In present study, we probed oxidation state in high-pressure transformation products Fe3+OOH goethite by situ X-ray absorption spectroscopy laser-heated diamond-anvil cell. At temperatures ~91 GPa 1,500-2,350 K, respectively, that is, reported stability field...
The structural environment of substitutional Cr3+ ion in a natural pyrope Mg3Al2Si3O12 has been investigated by Cr K-edge Extended X-ray Absorption Fine Structure (EXAFS) and Near Edge (XANES) coupled with first-principles computations. Cr-O distance is close to that knorringite Mg3Cr2Si3O12, indicating full relaxation the first neighbors. local C3i symmetry octahedral Y site retained during Cr-Al substitution. second third shells neighbors (Mg Si) relax only partially. Site accommodated...
We present a comparison between XANES experiments and full multiple-scattering calculations at the magnesium K-edge for two pyroxenes, diopside enstatite, which Mg atoms are only in M1 site distinct sites M2, respectively. The influence of number octahedral per unit cell distortion on spectra is investigated. Good agreement experiment obtained. Full permit identification contribution each site. Comparison reveals that enstatite have same profile. Cluster size analysis shows most features...
We present a reciprocal-space "non muffin-tin" scheme for calculating X-ray Absorption Near-Edge Structure (XANES). The method uses pseudopotentials and reconstructs all electron wave functions within the Projector Augmented Wave framework. incorporates recursive to compute absorption cross section as continued fraction. fraction formulation of is advantageous in that it permits treatment core-hole-electron interaction through large supercells (hundreds atoms). This opens new fields...
The structural environment of Mg in a K-bearing silicate glass composition K(2)MgSi(3)O(8) is investigated by x-ray absorption near-edge structure (XANES) spectroscopy at the K-edge. XANES calculations are performed using plane-wave electronic code, and model obtained classical molecular dynamics coupled to ab initio relaxation. Bond valence theory used validate plausible environments within models. Comparison between experimental calculated spectra enables us conclude that atoms located...