X-ray Raman Scattering Spectra Research Articles

Anomalous Impact of Mechanochemical Treatment on the Na-ion Conductivity of Sodium Closo-Carbadodecaborate Probed by X-Ray Raman Scattering Spectroscopy.

Solid-state sodium ion conductors are crucial for the next generation of all-solid-state sodium batteries with high capacity, low cost, and improved safety. Sodium closo-carbadodecaborate (NaCB11 H12 ) is an attractive Na-ion conductor owing to its high thermal, electrochemical, and interfacial stability. Mechanical milling has recently been shown to increase conductivity by five orders of magnitude at room temperature, making it appealing for application in all-solid-state sodium batteries. Intriguingly, milling longer than 2 h led to a significant decrease in conductivity. In this study, X-ray Raman scattering (XRS) spectroscopy is used to probe the origin of the anomalous impact of mechanical treatment on the ionic conductivity of NaCB11 H12 . The B, C, and Na K-edge XRS spectra are successfully measured for the first time, and ab initio calculations are employed to interpret the results. The experimental and computational results reveal that the decrease in ionic conductivity upon prolonged milling is due to the increased proximity of Na to the CB11 H12 cage, caused by severe distortion of the long-range structure. Overall, this work demonstrates how the XRS technique, allowing investigation of low Z elements such as C and B in the bulk, can be used to acquire valuable information on the electronic structure of solid electrolytes and battery materials in general.

A general overview and comparative interpretation on element‐specific X‐ray spectroscopy techniques:XPS,XAS,andXRS

AbstractX‐ray photoelectron spectroscopy (XPS), X‐ray absorption spectroscopy (XAS) and X‐ray Raman scattering (XRS) spectroscopy are the element‐specific tools providing local electronic and chemical structure insights. XPS is widely used for qualitative/quantitative surface analysis of solids and replaced by synchrotron‐based ambient pressure‐XPS and hard‐XPS to benefit from the advantages of near‐ambient pressures and hard X‐rays to study complex sample environments. XAS is a well‐established soft and hard X‐ray probe to examine the coordination, spin and oxidation states in solids, liquids and gases with high resolutions and short data acquisition time. XRS, using the hard X‐rays of ~10 keV, is preferred to conventional XAS and XPS in the study of soft X‐ray absorption edges such as C, O, Li K‐edges bulk‐sensitively in vacuum‐free medium for energy storage systems during working operations, inner Earth elements under realistic conditions, probing chemical and biological reactions in the liquid phase, C speciation in archeological and paleontological samples and direct tomography. In this study, first the basics of XPS, XAS, and XRS techniques with their advantages and limitations are introduced to provide a general overview. In the Results and Discussion, the particular emphasis is given to the comparison of XPS, XAS, and XRS with the interpretation of the spectroscopic signatures for organic carbonate‐based electrolytes. The computed C 1 s binding energy shifts for ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) are presented to discuss the XPS peak assignments and the performed C K‐edge XRS measurements of 1 M LiPF6in DMC and EC are given for a detailed discussion of the XRS spectra. C 1 s XPS, C K‐edge XAS, and XRS of PC from the literature are discussed to interpret the spectra of each technique comparatively.

Influence of partially occupied sites on the near-edge structure in [formula omitted]-rhombohedral boron: An X-ray Raman scattering study

A study of the near-edge structure at the K-edge of elemental boron in its β-rhombohedral phase is presented. Momentum-transfer dependent measurements of the B 1s core-electron excitation spectra were performed by X-ray Raman scattering (XRS) spectroscopy. Spectral features were interpreted based on calculations of the XRS spectra. A method to model a system with partially occupied sites (POS) was implemented based on FEFF simulations of XRS spectra. The inclusion of POS in the crystal structure of β-rhombohedral boron in the calculations was essential in order to achieve agreement between simulated and measured spectra. Transitions from the core-level to exo-icosahedron orbitals were found to be sensitive to the presence of partially occupied sites in β-rhombohedral boron. The origin and the momentum-transfer dependence of the spectral features are discussed. Characteristic spectral features from icosahedral units and from icosahedron clusters were identified. Activation of non-dipole transitions at high momentum transfers was detected.

Li 1s core exciton in LiH studied by x-ray Raman scattering spectroscopy

The Li 1s core excitation spectra in LiH was studied by means of x-ray Raman scattering (XRS) spectroscopy in a wide range of momentum transfers q. The analysis of the near-edge region of the measured spectra in combination with q-dependent ab initio calculations of XRS spectra based on the Bethe–Salpeter equation (BSE) reveals that the prominent peak at the excitation onset arises from two main contributions, namely a pre-edge peak associated to a p-type core exciton and strong transitions to empty states near the bottom of the conduction band, which is in contrast to previous experimental studies that attributed that feature to a single excitonic peak. The p-like angular symmetry of the core exciton is supported by BSE calculations of the relative contributions to the XRS spectra from monopole and dipole transitions and by the observed decrease of its normalised intensity for increasing momentum transfers. Higher energy spectral features in the measured XRS spectra are well reproduced by BSE, as well as by real-space multiple-scattering calculations.

First-principles modeling of x-ray Raman scattering spectra

X-ray Raman scattering (XRS) spectroscopy is a rapidly developing synchrotron-based technique employed to probe the local electronic structure of condensed matter. The use of hard x-rays makes XRS particularly well-suited for studying low-energy edges of bulk materials, even under highly absorbing sample environments, opening up a wealth of possibilities for $i\phantom{\rule{0}{0ex}}n$ $s\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}u$ experiments. Here, the authors propose an efficient method for calculating $K$-edge XRS spectra, developed within the framework of density functional theory and designed to fully account for the electric multipole transitions observed when a finite momentum is transferred to the photoelectron.

Core-hole Effect on Partial Electronic Density of State and O K-edge x-ray Raman Scattering Spectra of High-Pressure SiO2 Phases

Core-hole Effect on Partial Electronic Density of State and O K-edge x-ray Raman Scattering Spectra of High-Pressure SiO2 Phases

Planning, performing and analyzing X-ray Raman scattering experiments.

A compilation of procedures for planning and performing X-ray Raman scattering (XRS) experiments and analyzing data obtained from them is presented. In particular, it is demonstrated how to predict the overall shape of the spectra, estimate detection limits for dilute samples, and how to normalize the recorded spectra to absolute units. In addition, methods for processing data from multiple-crystal XRS spectrometers with imaging capability are presented, including a super-resolution method that can be used for direct tomography using XRS spectra as the contrast. An open-source software package with these procedures implemented is also made available.

X-ray Raman scattering provides evidence for interfacial acetonitrile-water dipole interactions in aqueous solutions

Aqueous solutions of acetonitrile (MeCN) have been studied with oxygen K-edge x-ray Raman scattering (XRS) which is found to be sensitive to the interaction between water and MeCN. The changes in the XRS spectra can be attributed to water directly interacting with MeCN and are reproduced by density functional theory calculations on small clusters of water and MeCN. The dominant structural arrangement features dipole interaction instead of H-bonds between the two species as revealed by the XRS spectra combined with spectrum calculations. Small-angle x-ray scattering shows the largest heterogeneity for a MeCN to water ratio of 0.4 in agreement with earlier small-angle neutron scattering data.

The structure of water in the hydration shell of cations from x-ray Raman and small angle x-ray scattering measurements.

X-ray Raman scattering (XRS) spectroscopy and small angle x-ray scattering (SAXS) are used to study water in aqueous solutions of NaCl, MgCl(2), and AlCl(3) with the particular aim to provide information about the structure of the hydration shells of the cations. The XRS spectra show that Na(+) weakens the hydrogen bonds of water molecules in its vicinity, similar to the effect of increased temperature and pressure. Mg(2+) and Al(3+), on the other hand, cause the formation of short and strong hydrogen bonds between the surrounding water molecules. The SAXS data show that Mg(2+) and Al(3+) form tightly bound hydration shells that give a large density contrast in the scattering data. From the form factors extracted from the SAXS data, we found that Mg(2+) and Al(3+) have, respectively, an equivalent of one and one and a half stable hydration shells that appear as a density contrast. In addition, we estimated that the density of water in the hydration shells of Mg(2+) and Al(3+) is, respectively, ∼61% and ∼71% higher than in bulk water.

X-ray Raman scattering for structural investigation of silica/silicate minerals

We have performed X-ray Raman scattering (XRS) measurements on the oxygen K and silicon L absorption edges of four silica minerals: α-quartz, α-cristobalite, coesite, and stishovite. We have also calculated the partial electron densities of states (DOSs) and compared these with the XRS spectra. This study demonstrates that the short-range structure around the atom of interest strongly influences the XRS spectral features. Importantly, the oxygen K-edge XRS spectra are found to reflect the p-orbital DOS while the silicon L-edge spectra reflect the s- and d-orbital DOSs, even when a product of a momentum transfer and a mean radius of a electron orbit (1s for oxygen and 2p for silicon), Qr, is close to or larger than unity. Building on this, calculations of the partial DOSs for other silica phases are presented, including ultra-high-pressure phases, which provide a good reference for further XRS study of silica and silicate minerals. XRS measurements should be performed on not only either of oxygen or silicon but also on many kinds of constituent elements to reveal the structural change of glasses/melts of silicates under extreme conditions.

Coordination environment of silicon in silica glass up to 74 GPa: An x-ray Raman scattering study at the siliconLedge

Near-edge x-ray Raman scattering (XRS) spectra of the silicon $L$ edge have been obtained on ${\text{SiO}}_{2}$ glass under compression in a diamond anvil cell up to 74 GPa. Partial densities of states (DOS's) of electrons, which the spectra reflect, have been calculated. The spectra for the glass do not show significant variations with pressure, whereas distinct differences are observed between quartz and stishovite, providing clear evidence for the nonexistence of sixfold-coordinated silicon by oxygen, that is stishovitelike silicon, in silica glass up to 74 GPa. A post main-edge hump, which is not seen in the XRS spectra and DOS's of quartz and stishovite, and an edge energy shift suggest that the silicon is in a different coordination environment under pressure. A compression mechanism of ${\text{SiO}}_{2}$ glass which involves the formation of fivefold-coordinated silicon following the decrease in Si-O-Si angle is proposed to explain the observed changes up to 74 GPa.

Role of inversion symmetry and multipole effects in nonresonant x-ray Raman scattering from icosahedralB4C

We report nonresonant x-ray Raman scattering (XRS) measurements for the icosahedral boron carbide ${\mathrm{B}}_{4}\mathrm{C}$ for transferred momentum q from 1 to 9 ${\mathrm{\AA{}}}^{\mathrm{\ensuremath{-}}1}$. The observed q-dependence together with site-specific ab initio calculations identify a near-edge peak in the XRS spectra as a p-type $(\ensuremath{\Delta}l=1)$ exciton due to dominant boron occupation at the sole atomic site in the unit cell having inversion symmetry. This result constrains models of substitutional disorder in ${\mathrm{B}}_{4}\mathrm{C},$ introduces a new application of XRS, and emphasizes the utility of full multiple scattering calculations of the site-specific projected density of states for interpretation of the near edge region of XRS spectra.