@article{KaaSternemannAppeletal.2022, author = {Kaa, Johannes M. and Sternemann, Christian and Appel, Karen and Cerantola, Valerio and Preston, Thomas R. and Albers, Christian and Elbers, Mirko and Libon, Lelia and Makita, Mikako and Pelka, Alexander and Petitgirard, Sylvain and Pl{\"u}ckthun, Christian and Roddatis, Vladimir and Sahle, Christoph J. and Spiekermann, Georg and Schmidt, Christian and Schreiber, Anja and Sakrowski, Robin and Tolan, Metin and Wilke, Max and Zastrau, Ulf and Konopkova, Zuzana}, title = {Structural and electron spin state changes in an x-ray heated iron carbonate system at the Earth's lower mantle pressures}, series = {Physical review research}, volume = {4}, journal = {Physical review research}, number = {3}, publisher = {American Physical Society}, address = {College Park}, issn = {2643-1564}, doi = {10.1103/PhysRevResearch.4.033042}, pages = {9}, year = {2022}, abstract = {The determination of the spin state of iron-bearing compounds at high pressure and temperature is crucial for our understanding of chemical and physical properties of the deep Earth. Studies on the relationship between the coordination of iron and its electronic spin structure in iron-bearing oxides, silicates, carbonates, iron alloys, and other minerals found in the Earth's mantle and core are scarce because of the technical challenges to simultaneously probe the sample at high pressures and temperatures. We used the unique properties of a pulsed and highly brilliant x-ray free electron laser (XFEL) beam at the High Energy Density (HED) instrument of the European XFEL to x-ray heat and probe samples contained in a diamond anvil cell. We heated and probed with the same x-ray pulse train and simultaneously measured x-ray emission and x-ray diffraction of an FeCO3 sample at a pressure of 51 GPa with up to melting temperatures. We collected spin state sensitive Fe K beta(1,3) fluorescence spectra and detected the sample's structural changes via diffraction, observing the inverse volume collapse across the spin transition. During x-ray heating, the carbonate transforms into orthorhombic Fe4C3O12 and iron oxides. Incipient melting was also observed. This approach to collect information about the electronic state and structural changes from samples contained in a diamond anvil cell at melting temperatures and above will considerably improve our understanding of the structure and dynamics of planetary and exoplanetary interiors.}, language = {en} } @article{PetitgirardSahleWeisetal.2019, author = {Petitgirard, Sylvian and Sahle, C. J. and Weis, C. and Gilmore, K. and Spiekermann, Georg and Tse, J. S. and Wilke, Max and Cavallari, C. and Cerantola, V and Sternemann, Christian}, title = {Magma properties at deep Earth's conditions from electronic structure of silica}, series = {Geochemical perspectives letters}, volume = {9}, journal = {Geochemical perspectives letters}, publisher = {Association of Geochemistry}, address = {Paris}, issn = {2410-339X}, doi = {10.7185/geochemlet.1902}, pages = {32 -- 37}, year = {2019}, abstract = {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.}, language = {en} } @article{WeisSpiekermannSternemannetal.2018, author = {Weis, Christopher and Spiekermann, Georg and Sternemann, Christian and Harder, Manuel and Vanko, Gyorgy and Cerantola, Valerio and Sahle, Christoph J. and Forov, Yury and Sakrowski, Robin and Kupenko, Ilya and Petitgirard, Sylvain and Yavas, Hasan and Bressler, Christian and Gawelda, Wojciech and Tolan, Metin and Wilke, Max}, title = {Combining X-ray K beta(1,3), valence-to-core, and X-ray Raman spectroscopy for studying Earth materials at high pressure and temperature}, series = {Journal of analytical atomic spectrometry}, volume = {34}, journal = {Journal of analytical atomic spectrometry}, number = {2}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {0267-9477}, doi = {10.1039/c8ja00247a}, pages = {384 -- 393}, year = {2018}, abstract = {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.}, language = {en} } @article{WeisSternemannCerantolaetal.2017, author = {Weis, Christopher and Sternemann, Christian and Cerantola, Valerio and Sahle, Christoph J. and Spiekermann, Georg and Harder, Manuel and Forov, Yury and Kononov, Alexander and Sakrowski, Robin and Yavas, Hasan and Tolan, Metin and Wilke, Max}, title = {Pressure driven spin transition in siderite and magnesiosiderite single crystals}, series = {Scientific reports}, volume = {7}, journal = {Scientific reports}, publisher = {Nature Publ. Group}, address = {London}, issn = {2045-2322}, doi = {10.1038/s41598-017-16733-3}, pages = {10}, year = {2017}, language = {en} } @article{SahleNiskanenSchmidtetal.2017, author = {Sahle, Christoph J. and Niskanen, Johannes and Schmidt, Christian and Stefanski, Johannes and Gilmore, Keith and Forov, Yury and Jahn, Sandro and Wilke, Max and Sternemann, Christian}, title = {Cation Hydration in Supercritical NaOH and HCl Aqueous Solutions}, series = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, volume = {121}, journal = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, publisher = {American Chemical Society}, address = {Washington}, issn = {1520-6106}, doi = {10.1021/acs.jpcb.7b09688}, pages = {11383 -- 11389}, year = {2017}, abstract = {We present a study of the local atomic environment of the oxygen atoms in the aqueous solutions of NaOH and HCl under simultaneous high-temperature and high-pressure conditions. Experimental nonresonant X-ray Raman scattering core-level spectra at the oxygen K-edge show systematic changes as a function of temperature and pressure. These systematic changes are distinct for the two different solutes and are described well by calculations within the Bethe- Salpeter formalism for snapshots from ab initio molecular dynamics simulations. The agreement between experimental and simulation results allows us to use the computations for a detailed fingerprinting analysis in an effort to elucidate the local atomic structure and hydrogen-bonding topology in these relevant solutions. We observe that both electrolytes, especially NaOH, enhance hydrogen bonding and tetrahedrality in the water structure at supercritical conditions, in particular in the vicinity of the hydration shells. This effect is accompanied with the association of the HCl and NaOH molecules at elevated temperatures.}, language = {en} } @misc{SpiekermannHarderGilmoreetal.2019, author = {Spiekermann, Georg and Harder, M. and Gilmore, Keith and Zalden, Peter and Sahle, Christoph J. and Petitgirard, Sylvain and Wilke, Max and Biedermann, Nicole and Weis, Thomas and Morgenroth, Wolfgang and Tse, John S. and Kulik, E. and Nishiyama, Norimasa and Yava{\c{s}}, Hasan and Sternemann, Christian}, title = {Persistent Octahedral Coordination in Amorphous GeO₂ Up to 100 GPa by Kβ'' X-Ray Emission Spectroscopy}, series = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, number = {699}, issn = {1866-8372}, doi = {10.25932/publishup-42775}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-427755}, year = {2019}, abstract = {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.}, language = {en} } @article{SpiekermannHarderGilmoreetal.2019, author = {Spiekermann, Georg and Harder, M. and Gilmore, Keith and Zalden, Peter and Sahle, Christoph J. and Petitgirard, Sylvain and Wilke, Max and Biedermann, Nicole and Weis, Thomas and Morgenroth, Wolfgang and Tse, John S. and Kulik, E. and Nishiyama, Norimasa and Yava{\c{s}}, Hasan and Sternemann, Christian}, title = {Persistent Octahedral Coordination in Amorphous GeO₂ Up to 100 GPa by Kβ'' X-Ray Emission Spectroscopy}, series = {Physical Review X}, volume = {9}, journal = {Physical Review X}, number = {1}, publisher = {American Physical Society by the American Institute of Physics}, address = {Melville, NY}, issn = {2469-9926}, doi = {10.1103/PhysRevX.9.011025}, pages = {10}, year = {2019}, abstract = {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.}, language = {en} }