TY - JOUR A1 - Weis, Christopher A1 - Sternemann, Christian A1 - Cerantola, Valerio A1 - Sahle, Christoph J. A1 - Spiekermann, Georg A1 - Harder, Manuel A1 - Forov, Yury A1 - Kononov, Alexander A1 - Sakrowski, Robin A1 - Yavas, Hasan A1 - Tolan, Metin A1 - Wilke, Max T1 - Pressure driven spin transition in siderite and magnesiosiderite single crystals JF - Scientific reports Y1 - 2017 U6 - https://doi.org/10.1038/s41598-017-16733-3 SN - 2045-2322 VL - 7 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Weis, Christopher A1 - Spiekermann, Georg A1 - Sternemann, Christian A1 - Harder, Manuel A1 - Vanko, Gyorgy A1 - Cerantola, Valerio A1 - Sahle, Christoph J. A1 - Forov, Yury A1 - Sakrowski, Robin A1 - Kupenko, Ilya A1 - Petitgirard, Sylvain A1 - Yavas, Hasan A1 - Bressler, Christian A1 - Gawelda, Wojciech A1 - Tolan, Metin A1 - Wilke, Max T1 - Combining X-ray K beta(1,3), valence-to-core, and X-ray Raman spectroscopy for studying Earth materials at high pressure and temperature BT - the case of siderite JF - Journal of analytical atomic spectrometry N2 - X-ray emission and X-ray Raman scattering spectroscopy are powerful tools to investigate the local electronic and atomic structure of high and low Z elements in situ. Notably, these methods can be applied for in situ spectroscopy at high pressure and high temperature using resistively or laser-heated diamond anvil cells in order to achieve thermodynamic conditions which appear in the Earth's interior. We present a setup for combined X-ray emission and X-ray Raman scattering studies at beamline P01 of PETRA III using a portable wavelength-dispersive von Hamos spectrometer together with the permanently installed multiple-analyzer Johann-type spectrometer. The capabilities of this setup are exemplified by investigating the iron spin crossover of siderite FeCO3 up to 49.3 GPa by measuring the Fe M2,3-edge and the Fe Kβ1,3 emission line simultaneously. With this setup, the Fe valence-to-core emission can be detected together with the Kβ1,3 emission line providing complementary information on the sample's electronic structure. By implementing a laser-heating device, we demonstrate the strength of using a von Hamos type spectrometer for spin state mapping at extreme conditions. Finally, we give different examples of low Z elements' absorption edges relevant for application in geoscience that are accessible with the Johann-type XRS spectrometer. With this setup new insights into the spin transition and compression mechanisms of Earth's mantle materials can be obtained of importance for comprehension of the macroscopic physical and chemical properties of the Earth's interior. Y1 - 2018 U6 - https://doi.org/10.1039/c8ja00247a SN - 0267-9477 SN - 1364-5544 VL - 34 IS - 2 SP - 384 EP - 393 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Sublett, David Matthew A1 - Sendula, Eszter A1 - Lamadrid, Hector A1 - Steele-MacInnis, Matthew A1 - Spiekermann, Georg A1 - Burruss, Robert C. A1 - Bodnar, Robert J. T1 - Shift in the Raman symmetric stretching band of N-2, CO2, and CH4 as a function of temperature, pressure, and density JF - Journal of Raman spectroscopy : JRS N2 - The Raman spectra of pure N-2, CO2, and CH4 were analyzed over the range 10 to 500 bars and from -160 degrees C to 200 degrees C (N-2), 22 degrees C to 350 degrees C (CO2), and -100 degrees C to 450 degrees C (CH4). At constant temperature, Raman peak position, including the more intense CO2 peak (nu+), decreases (shifts to lower wave number) with increasing pressure for all three gases over the entire pressure and temperature (PT) range studied. At constant pressure, the peak position for CO2 and CH4 increases (shifts to higher wave number) with increasing temperature over the entire PT range studied. In contrast, N-2 first shows an increase in peak position with increasing temperature at constant pressure, followed by a decrease in peak position with increasing temperature. The inflection temperature at which the trend reverses for N-2 is located between 0 degrees C and 50 degrees C at pressures above similar to 50 bars and is pressure dependent. Below similar to 50 bars, the inflection temperature was observed as low as -120 degrees C. The shifts in Raman peak positions with PT are related to relative density changes, which reflect changes in intermolecular attraction and repulsion. A conceptual model relating the Raman spectral properties of N-2, CO2, and CH4 to relative density (volume) changes and attractive and repulsive forces is presented here. Additionally, reduced temperature-dependent densimeters and barometers are presented for each pure component over the respective PT ranges. The Raman spectral behavior of the pure gases as a function of temperature and pressure is assessed to provide a framework for understanding the behavior of each component in multicomponent N-2-CO2-CH4 gas systems in a future study. KW - fluids KW - wave number KW - attraction KW - repulsion Y1 - 2019 U6 - https://doi.org/10.1002/jrs.5805 SN - 0377-0486 SN - 1097-4555 VL - 51 IS - 3 SP - 555 EP - 568 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Spiekermann, Georg A1 - Wilke, Max A1 - Jahn, Sandro T1 - Structural and dynamical properties of supercritical H2O-SiO2 fluids studied by ab initio molecular dynamics JF - Chemical geology : official journal of the European Association for Geochemistry N2 - In this study we report the structure of supercritical H2O-SiO2 fluid composed of 50 mol% H2O and 50 mol% SiO2 at 3000 K and 2400 K. investigated by means of ab initio molecular dynamics of models comprising 192 and 96 atoms. The density is set constant to 138 g/cm(3), which yields a pressure of 4.3 GPa at 3000 K and 3.6 GPa at 2400 K. Throughout the trajec[ories, water molecules are formed and dissociated via the network modifying reaction 2 SiOH = SiOSi + H2O The calculation of the reaction constant K- [OH](2)/[H2O][O2-] is carried out on the basis of the experimentally relevant Q ' species notation and agrees well with an extrapolation of experimental data to 3000 K. After quench from 3000 K to 2400 K, the degree of polymerization of the silicate network in the 192-atom models increases noticeably within several tens of picoseconds, accompanied by release of molecular H2O. An unexpected opposite trend is observed in smaller 96-atom models, due to a finite size effect, as several uncorrelated models of 192 and 96 atoms indicate. The temperature-dependent slowing down of the H2O-silica interaction dynamics is described on the basis of the bond autocorrelation function. (C) 2016 Elsevier B.V. All rights reserved. KW - Fluid KW - SiO2-H2O KW - SiO(2)Molecular dynamics KW - Polymerization KW - DFT Y1 - 2016 U6 - https://doi.org/10.1016/j.chemgeo.2016.01.010 SN - 0009-2541 SN - 1878-5999 VL - 426 SP - 85 EP - 94 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Spiekermann, Georg A1 - Harder, M. A1 - Gilmore, Keith A1 - Zalden, Peter A1 - Sahle, Christoph J. A1 - Petitgirard, Sylvain A1 - Wilke, Max A1 - Biedermann, Nicole A1 - Weis, Thomas A1 - Morgenroth, Wolfgang A1 - Tse, John S. A1 - Kulik, E. A1 - Nishiyama, Norimasa A1 - Yavaş, Hasan A1 - Sternemann, Christian T1 - Persistent Octahedral Coordination in Amorphous GeO₂ Up to 100 GPa by Kβ'' X-Ray Emission Spectroscopy JF - Physical Review X N2 - We measure valence-to-core x-ray emission spectra of compressed crystalline GeO₂ up to 56 GPa and of amorphous GeO₂ up to 100 GPa. In a novel approach, we extract the Ge coordination number and mean Ge-O distances from the emission energy and the intensity of the Kβ'' emission line. The spectra of high-pressure polymorphs are calculated using the Bethe-Salpeter equation. Trends observed in the experimental and calculated spectra are found to match only when utilizing an octahedral model. The results reveal persistent octahedral Ge coordination with increasing distortion, similar to the compaction mechanism in the sequence of octahedrally coordinated crystalline GeO₂ high-pressure polymorphs. KW - rutile-type KW - glass KW - crystalline KW - pressures KW - complexes KW - silicon KW - oxygen KW - SIO₂ KW - MO KW - CU Y1 - 2019 U6 - https://doi.org/10.1103/PhysRevX.9.011025 SN - 2469-9926 SN - 0556-2791 SN - 1050-2947 SN - 1094-1622 VL - 9 IS - 1 PB - American Physical Society by the American Institute of Physics CY - Melville, NY ER - TY - JOUR A1 - Petitgirard, Sylvian A1 - Sahle, C. J. A1 - Weis, C. A1 - Gilmore, K. A1 - Spiekermann, Georg A1 - Tse, J. S. A1 - Wilke, Max A1 - Cavallari, C. A1 - Cerantola, V A1 - Sternemann, Christian T1 - Magma properties at deep Earth’s conditions from electronic structure of silica JF - Geochemical perspectives letters N2 - SiO(2 )is the main component of silicate melts and thus controls their network structure and physical properties. The compressibility and viscosities of melts at depth are governed by their short range atomic and electronic structure. We measured the O K-edge and the Si L-2,L-3-edge in silica up to 110 GPa using X-ray Raman scattering spectroscopy, and found a striking match to calculated spectra based on structures from molecular dynamic simulations. Between 20 and 27 GPa, Si-[4] species are converted into a mixture of Si-[5] and Si-[6] species and between 60 and 70 GPa, Si-[6] becomes dominant at the expense of Si-[5] with no further increase up to at least 110 GPa. Coordination higher than 6 is only reached beyond 140 GPa, corroborating results from Brillouin scattering. Network modifying elements in silicate melts may shift this change in coordination to lower pressures and thus magmas could be denser than residual solids at the depth of the core-mantle boundary. Y1 - 2019 U6 - https://doi.org/10.7185/geochemlet.1902 SN - 2410-339X SN - 2410-3403 VL - 9 SP - 32 EP - 37 PB - Association of Geochemistry CY - Paris ER - TY - JOUR A1 - Petitgirard, Sylvain A1 - Spiekermann, Georg A1 - Glazyrin, Konstantin A1 - Garrevoet, Jan A1 - Murakami, Motohiko T1 - Density of amorphous GeO2 to 133 GPa with possible pyritelike structure and stiffness at high pressure JF - Physical review : B, Condensed matter and materials physics N2 - Germanium oxide is a prototype network-forming oxide with pressure-induced structural changes similar to those found in crystals and amorphous silicate oxides at high pressure. Studying density and coordination changes in amorphous GeO2 allows for insight into structural changes in silicate oxides at very high pressure, with implications for the properties of planetary magmas. Here, we report the density of germanium oxide glass up to 133 GPa using the x-ray absorption technique, with very good agreement with previous experimental data at pressure below 40 GPa and recent calculation up to 140 GPa. Our data highlight four distinct compressibility domains, corresponding to changes of the local structure of GeO2. Above 80 GPa, our density data show a compressibility and bulk modulus similar to the counterpart crystal phase, and we propose that a compact distorted sixfold coordination, similar to the structural motif of the pyritelike crystalline GeO2 polymorph, is likely to be stable in that pressure range. Our density data point to a smooth continuous evolution of the average coordination for pressure above 20 GPa with persistent sixfold coordination, without sharp density or density slope discontinuities. These observations are in very good agreement with theoretical calculations and spectroscopic measurements, and our results indicate that glasses and melts may behave similarly to their high-pressure solid counterparts with comparable densities, compressibility, and possibly average coordination. Y1 - 2019 U6 - https://doi.org/10.1103/PhysRevB.100.214104 SN - 2469-9950 SN - 2469-9969 VL - 100 IS - 21 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Ketenoglu, Didem A1 - Spiekermann, Georg A1 - Harder, Manuel A1 - Oz, Erdinc A1 - Koz, Cevriye A1 - Yagci, Mehmet C. A1 - Yilmaz, Eda A1 - Yin, Zhong A1 - Sahle, Christoph J. A1 - Detlefs, Blanka A1 - Yavas, Hasan T1 - X-ray Raman spectroscopy of lithium-ion battery electrolyte solutions in a flow cell JF - Journal of synchrotron radiation N2 - The effects of varying LiPF6 salt concentration and the presence of lithium bis(oxalate)borate additive on the electronic structure of commonly used lithium-ion battery electrolyte solvents (ethylene carbonate-dimethyl carbonate and propylene carbonate) have been investigated. X-ray Raman scattering spectroscopy (a non-resonant inelastic X-ray scattering method) was utilized together with a closed-circle flow cell. Carbon and oxygen K-edges provide characteristic information on the electronic structure of the electrolyte solutions, which are sensitive to local chemistry. Higher Li+ ion concentration in the solvent manifests itself as a blue-shift of both the pi* feature in the carbon edge and the carbonyl pi* feature in the oxygen edge. While these oxygen K-edge results agree with previous soft X-ray absorption studies on LiBF4 salt concentration in propylene carbonate, carbon K-edge spectra reveal a shift in energy, which can be explained with differing ionic conductivities of the electrolyte solutions. KW - non-resonant inelastic X-ray scattering KW - lithium-ion battery electrolyte KW - C and O K-edge spectra Y1 - 2018 U6 - https://doi.org/10.1107/S1600577518001662 SN - 0909-0495 SN - 1600-5775 VL - 25 SP - 537 EP - 542 PB - International Union of Crystallography CY - Chester ER -