TY - JOUR A1 - Wilke, Max T1 - X-Ray Absorption Spectroscopy Measurements JF - Magmas Under Pressure : Advances in High-Pressure Experiments on Structure and Properties of Melts N2 - An overview is given on the current state of X-ray absorption measurements on silicate melts and glasses. The challenges, limitations, and achievements of analyzing X-ray absorption spectra measured in liquids to determine structural properties of major and minor elements in magmas are described, with particular focus on describing non-Gaussian pair distribution functions in highly disordered glasses and melts, measured at in situ conditions. This includes a discussion on the progress of combining experiments with data from molecular dynamics simulations. For the measurements at conditions of the deep Earth, various experimental approaches and necessities are discussed and two examples are described in more detail. Finally, the achievements and prospects are presented for measuring X-ray absorption spectra indirectly by X-ray Raman scattering. Y1 - 2018 SN - 978-0-12-811274-8 SN - 978-0-12-811301-1 U6 - https://doi.org/10.1016/B978-0-12-811301-1.00006-X SP - 155 EP - 178 PB - Elsevier CY - Amsterdam 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 - Pohlenz, Julia A1 - Rosa, A. D. A1 - Mathon, O. A1 - Pascarelli, S. A1 - Belin, S. A1 - Landrot, G. A1 - Murzin, V. A1 - Veligzhanin, A. A1 - Shiryaev, A. A1 - Irifune, T. A1 - Wilke, Max T1 - Structural controls of CO2 on Y, La and Sr incorporation in sodium-rich silicate - carbonate melts by in-situ high P-T EXAFS JF - Chemical geology : official journal of the European Association for Geochemistry N2 - Carbonate-rich silicate and carbonate melts play a crucial role in deep Earth magmatic processes and their melt structure is a key parameter, as it controls physical and transport properties. Carbon-rich melts can be strongly enriched in trace elements, but the structural incorporation mechanisms of these elements are difficult to study because such melts generally cannot be quenched to glasses. In this contribution we investigate the influence of CO2 on the local environments of trace elements contained in silicate glasses with variable CO2 concentrations and in silicate and carbonate melts. The melts were studied in-situ at high pressure and temperature conditions using the Paris-Edinburgh press (2.2 to 2.6 GPa and 1200 to 1500 degrees C). The compositions studied include sodium-rich peralkaline silicate melts and glasses and carbonate melts similar to those occurring naturally at Oldoinyo Lengai volcano. The local environments of yttrium (Y), lanthanum (La) and strontium (Sr) were investigated using extended X-ray absorption fine structure (EXAFS) spectroscopy. Main findings of the study suggest: (1) In peralkaline silicate glasses the local structure of Y is unaffected by the CO2 content. Contrary, a slight increase of oxygen bond lengths of Sr and La is inferred with increasing CO2 content in peralkaline glasses, while they remain constant in glasses of even higher peralkalinity independent of the CO2 content. (2) In silicate melts of different CO2 contents Y-O bond lengths are constant, while a slight increase within carbonate melt compositions is deduced. On the other hand, a steady bond lengths increase over the whole compositional range is inferred for La-O and Sr-O. This may well be explained by distinct preferences of these elements for specific local environments. Based on these new data, we suggest potential mechanisms for the structural incorporation of these elements, a key step towards understanding their partitioning behavior in natural magmatic systems. KW - Silicate- carbonate melts/glasses KW - Local structure Yttrium, Strontium, Lanthanum KW - EXAFS KW - Paris-Edinburgh press Y1 - 2018 U6 - https://doi.org/10.1016/j.chemgeo.2017.12.023 SN - 0009-2541 SN - 1872-6836 VL - 486 SP - 1 EP - 15 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Nunez Valdez, Maribel A1 - Efthimiopoulos, Ilias A1 - Taran, Michail A1 - Mueller, Jan A1 - Bykova, Elena A1 - McCammon, Catherine A1 - Koch-Müller, Monika A1 - Wilke, Max T1 - Evidence for a pressure-induced spin transition in olivine-type LiFePO4 triphylite JF - Physical review : B, Condensed matter and materials physics N2 - We present a combination of first-principles and experimental results regarding the structural and magnetic properties of olivine-type LiFePO4 under pressure. Our investigations indicate that the starting Pbnm phase of LiFePO4 persists up to 70 GPa. Further compression leads to an isostructural transition in the pressure range of 70-75 GPa, inconsistent with a former theoretical study. Considering our first-principles prediction for a high-spin to low-spin transition of Fe2+ close to 72 GPa, we attribute the experimentally observed isostructural transition to a change in the spin state of Fe2+ in LiFePO4. Compared to relevant Fe-bearing minerals, LiFePO4 exhibits the largest onset pressure for a pressure-induced spin state transition. Y1 - 2018 U6 - https://doi.org/10.1103/PhysRevB.97.184405 SN - 2469-9950 SN - 2469-9969 VL - 97 IS - 18 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Kutzschbach, Martin A1 - Guttmann, Peter A1 - Marquardt, K. A1 - Werner, S. A1 - Henzler, K. D. A1 - Wilke, Max T1 - A transmission x-ray microscopy and NEXAFS approach for studying corroded silicate glasses at the nanometre scale JF - European journal of glass science and technology / Deutsche Glastechnische Gesellschaft (DGG) and the Society of Glass Technology (SGT). B, Physics and chemistry of glasses N2 - In this study transmission X-ray microscopy (TXM) was tested as a method to investigate the chemistry and structure of corroded silicate glasses at the nanometer scale. Three different silicate glasses were altered in static corrosion experiments for 1-336 hours at temperatures between 60 degrees C and 85 degrees C using a 25% HCl solution. Thin lamellas were cut perpendicular to the surface of corroded glass monoliths and were analysed with conventional TEM as well as with TXM. By recording optical density profiles at photon energies around the Na and O K-edges, the shape of the corrosion rim/pristine glass interfaces and the thickness of the corrosion rims has been determined. Na and O near-edge X-ray absorption fine-structure spectra (NEXAFS) were obtained without inducing irradiation damage and have been used to detect chemical changes in the corrosion rims. Spatially resolved NEXAFS spectra at the O K-edge provided insight to structural changes in the corrosion layer on the atomic scale. By comparison to O K-edge spectra of silicate minerals and (hydrous) albite glass as well as to O K-edge NEXAFS of model structures simulated with ab initio calculations, evidence is provided that changes of the fine structure at the O K-edge are assigned to the formation of siloxane groups in the corrosion rim. Y1 - 2018 U6 - https://doi.org/10.13036/17533562.59.1.043 SN - 1753-3562 VL - 59 IS - 1 SP - 11 EP - 26 PB - Society of Glass Technology CY - Sheffield ER - TY - JOUR A1 - Dietrich, Marcel A1 - Behrens, Harald A1 - Wilke, Max T1 - A new optical cell for in situ Raman spectroscopy, and its application to study sulfur-bearing fluids at elevated pressures and temperatures JF - American mineralogist : an international journal of earth and planetary materials N2 - Sulfur is an important component in volcanic gases at the Earth surface but also present in the deep Earth in hydrothermal or magmatic fluids. Little is known about the evolution of such fluids during ascent in the crust. A new optical cell was developed for in situ Raman spectroscopic investigations on fluids allowing abrupt or continuous changes of pressure up to 200 MPa at temperatures up to 750 degrees C. The concept is based on a flexible gold bellow, which separates the sample fluid from the pressure medium water. To avoid reactions between aggressive fluids and the pressure cell, steel components in contact with the fluid are shielded by gold foil. The cell was tested to study redox reactions in fluids using aqueous ammonium sulfate solutions as a model system. During heating at constant pressure of 130 MPa, sulfate ions transform first to HSO4- ions and then to molecular units such as H2SO4. Variation of pressure shows that the stability of sulfate species relies on fluid density, i.e., highly charged species are stable only in high-density fluids. Partial decomposition of ammonium was evident above 550 degrees C by the occurrence of a nitrogen peak in the Raman spectra. Reduced sulfur species were observed above 700 degrees C by Raman signals near 2590 cm(-1) assigned to HS- and H2S. No clear evidence for the formation of sulfur dioxide was found in contrary to previous studies on aqueous H2SO4, suggesting very reducing conditions in our experiments. Fluid-mineral interaction was studied by inserting into the cell a small, semi-open capsule filled with a mixture of pyrite and pyrrhotite. Oxidation of the sample assembly was evident by transformation of pyrite to pyrrhotite. As a consequence, sulfide species were observed in the fluid already at temperatures of similar to 600 degrees C. KW - In situ Raman spectroscopy KW - fluids KW - decompression KW - optical cell KW - sulfur speciation KW - redox reactions Y1 - 2018 U6 - https://doi.org/10.2138/am-2018-6244 SN - 0003-004X SN - 1945-3027 VL - 103 IS - 3 SP - 418 EP - 429 PB - Mineralogical Society of America CY - Chantilly ER - TY - JOUR A1 - Benard, Antoine A1 - Klimm, Kevin A1 - Woodland, Alan B. A1 - Arculus, Richard J. A1 - Wilke, Max A1 - Botcharnikov, Roman E. A1 - Shimizu, Nobumichi A1 - Nebel, Oliver A1 - Rivard, Camille A1 - Ionov, Dmitri A. T1 - Oxidising agents in sub-arc mantle melts link slab devolatilisation and arc magmas JF - Nature Communications N2 - Subduction zone magmas are more oxidised on eruption than those at mid-ocean ridges. This is attributed either to oxidising components, derived from subducted lithosphere (slab) and added to the mantle wedge, or to oxidation processes occurring during magma ascent via differentiation. Here we provide direct evidence for contributions of oxidising slab agents to melts trapped in the sub-arc mantle. Measurements of sulfur (S) valence state in sub-arc mantle peridotites identify sulfate, both as crystalline anhydrite (CaSO4) and dissolved SO42- in spinel-hosted glass (formerly melt) inclusions. Copper-rich sulfide precipitates in the inclusions and increased Fe3+/Sigma Fe in spinel record a S6+-Fe2+ redox coupling during melt percolation through the sub-arc mantle. Sulfate-rich glass inclusions exhibit high U/Th, Pb/Ce, Sr/Nd and delta S-34 (+ 7 to + 11%), indicating the involvement of dehydration products of serpentinised slab rocks in their parental melt sources. These observations provide a link between liberated slab components and oxidised arc magmas. Y1 - 2018 U6 - https://doi.org/10.1038/s41467-018-05804-2 SN - 2041-1723 VL - 9 PB - Nature Publ. Group CY - London ER -