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Despite its ubiquitous nature, the atomic structure of water in its liquid state is still controversially debated. We use a combination of X-ray Raman scattering spectroscopy in conjunction with ab initio and path integral molecular dynamics simulations to study the local atomic and electronic structure of water under high pressure conditions. Systematically increasing fingerprints of non-hydrogen-bonded H2O molecules in the first hydration shell are identified in the experimental and computational oxygen K-edge excitation spectra. This provides evidence for a compaction mechanism in terms of a continuous collapse of the second hydration shell with increasing pressure via generation of interstitial water within locally tetrahedral hydrogen-bonding environments. [ABSTRACT FROM AUTHOR]

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 (NaCB11H12) 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 NaCB11H12. 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 CB11H12 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. [ABSTRACT FROM AUTHOR]

We present a new diamond anvil cell design, hereafter called mBX110, that combines both the advantages of a membrane and screws to generate high pressure. It enables studies at large-scale facilities for many synchrotron X-ray techniques and has the possibility to remotely control the pressure with the membrane as well as the use of the screws in the laboratory. It is fully compatible with various gas-loading systems as well as high/low temperature environments in the lab or at large scale facilities. The mBX110 possesses an opening angle of 85° suitable for single-crystal diffraction or Brillouin spectroscopy and a large side opening of 110° which can be used for X-ray inelastic techniques, such as X-ray Raman scattering spectroscopy, but also for X-ray emission, X-ray fluorescence, or X-ray absorption. An even larger opening of 150° can be manufactured enabling X-ray imaging tomography. We report data obtained with the mBX110 on different beamlines with single-crystal diffraction of stishovite up to 55 GPa, X-ray powder diffraction of rutile-GeO2 and tungsten to 25 GPa and 280 GPa, respectively, X-Ray Raman spectra of the Si L-edge in silica to 95 GPa, and Fe Kβ X-ray emission spectra on a basalt glass to 17 GPa. [ABSTRACT FROM AUTHOR]

We report on the microscopic structure of water at sub- and super-critical conditions studied using X-ray Raman spectroscopy, ab initio molecular dynamics simulations, and density functional theory. Systematic changes in the X-ray Raman spectra with increasing pressure and temperature are observed. Throughout the studied thermodynamic range, the experimental spectra can be interpreted with a structural model obtained from the molecular dynamics simulations. A spatial statistical analysis using Ripley's K-function shows that this model is homogeneous on the nanometer length scale. According to the simulations, distortions of the hydrogen-bond network increase dramatically when temperature and pressure increase to the supercritical regime. In particular, the average number of hydrogen bonds per molecule decreases to ≈0.6 at 600°C and p = 134 MPa. [ABSTRACT FROM AUTHOR]

A classic example of solid-state topochemical reactions is the ultraviolet-light induced photodimerization of α-trans-cinnamic acid (CA). Here, we report the first observation of an X-ray-induced dimerization of CA and monitor it in situ using nonresonant inelastic X-ray scattering spectroscopy (NRIXS). The time-evolution of the carbon core-electron excitation spectra shows the effects of two X-ray induced reactions: dimerization on a short time-scale and disintegration on a long time-scale. We used spectrum simulations of CA and its dimerization product, α-truxillic acid (TA), to gain insight into the dimerization effects. From the time-resolved spectra, we extracted component spectra and time-dependent weights corresponding to CA and TA. The results suggest that the X-ray induced dimerization proceeds homogeneously in contrast to the dimerization induced by ultraviolet light. We also utilized the ability of NRIXS for direct tomography with chemical-bond contrast to image the spatial progress of the reactions in the sample crystal. Our work paves the way for other time-resolved studies on chemical reactions using inelastic X-ray scattering. [ABSTRACT FROM AUTHOR]

We characterize experimentally and theoretically the collective electronic excitations in two prototypical layered transition-metal dichalcogenides, NbSe2 and Cu0.2NbS2. The energy- and momentum-dependent dynamical structure factor was measured by inelastic x-ray scattering (IXS) spectroscopy and simulated by time-dependent density-functional theory. We hnd good agreement between theory and experiment, provided that Nb semicore states are taken into account together with crystal local-held effects. Both materials have very similar spectra, characterized by two main plasmons at 9 and 23 eV, which we show to both have π + σ character on the basis of a detailed analysis of the band structure. Finally, we discuss the role of the layer anisotropy in the dispersion of these plasmons. [ABSTRACT FROM AUTHOR]

Carbon compounds are ubiquitous and occur in a diversity of chemical forms in many systems including ancient and historic materials ranging from cultural heritage to paleontology. Determining their speciation cannot only provide unique information on their origin but may also elucidate degradation processes. Synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy at the carbon K-edge (280-350 eV) is a very powerful method to probe carbon speciation. However, the short penetration depth of soft X-rays imposes stringent constraints on sample type, preparation, and analytical environment. A hard Xray probe such as X-ray Raman scattering (XRS) can overcome many of these difficulties. Here we report the use of XRS at ~6 keV incident energy to collect carbon K-edge XANES data and probe the speciation of organic carbon in several specimens relevant to cultural heritage and natural history. This methodology enables the measurement to be done in a nondestructive way, in air, and provides information that is not compromised by surface contamination by ensuring that the dominant signal contribution is from the bulk of the probed material. Using the backscattering geometry at large photon momentum transfer maximizes the XRS signal at the given X-ray energy and enhances nondipole contributions compared to conventional XANES, thereby augmenting the speciation sensitivity. The capabilities and limitations of the technique are discussed. We show that despite its small cross section, for a range of systems the XRS method can provide satisfactory signals at realistic experimental conditions. XRS constitutes a powerful complement to FT-IR, Raman, and conventional XANES spectroscopy, overcoming some of the limitations of these techniques. [ABSTRACT FROM AUTHOR]

We report a study on the hydrogen-bondnetwork of water in aqueousLiCl solutions using X-ray Raman scattering (XRS) spectroscopy. Awide concentration range of 0–17 mol/kg was covered. We findthat the XRS spectral features change systematically at low concentrationsand saturate at 11 mol/kg. This behavior suggests a gradual destructionin the hydrogen-bond network until the saturation concentration. Thesurprisingly large concentration required for the saturation supportsan interpretation in which the ions affect the structure of wateronly within their first hydration shell. The study is complementedby density-functional-theory calculations and molecular dynamics simulations. [ABSTRACT FROM AUTHOR]