Non-resonant and resonant X-ray emission at high pressure using a von Hámos setup: the case of FeO

The International Conference on Synchrotron Radiation Instrumentation (SRI) is a unique and significant international forum held every three years in the community of synchrotron radiation (SR) and free electron lasers (FEL). It is the prime forum for fostering connections between cutting-edge synchrotron radiation instrumentation, science, and the requirements of the user community. The SRI 2021 had originally been scheduled to take place in Hamburg in summer 2021. Due to the COVID-19 pandemic, it was postponed to 2022 and held as an online event.More than 1160 international participants from 25 countries met virtually at the SRI 2021. In nearly 290 talks and 450 posters, latest results were presented. Although it was an online-only conference, lively discussions took place in the nearly 40 parallel sessions, and the eight poster sessions were also very well attended.The main topics of the SRI conference were: new SR and FEL facilities, update plans of these facilities, and recent developments in various instrumentation areas like beamline design, X-ray optics, sample environments, detectors and spectrometers, data acquisition, and data analysis techniques or automation. These innovations contributed to new results for a wide range of experimental techniques and scientific applications such as X-ray scattering and spectroscopy, bio- and scanning imaging, structural biology crystallography, coherent techniques, or in-situ/operando methods. A dedicated session concerned industrial applications of synchrotron radiation.The field of synchrotron radiation instrumentation is currently seeing very active development due to various factors. Firstly, the number of SR sources world-wide is increasing significantly, with new sources in particular in Europe and in Asia. Secondly, a new generation of storage rings with new multi-bend achromat lattices are being implemented at a growing number of existing facilities. These facilities offer a significant increase of brilliance and coherence and thereby lead to new and improved applications of synchrotron radiation, in particular in the areas of imaging and high spatial resolution. Thirdly, the increase of soft and hard X-ray FEL sources worldwide and the maturation of their experimental techniques and scientific applications is the background for a strongly increasing number of developments for ultrafast time-resolved investigations of dynamic behaviour of materials and reactions. Most of the keynote speakers and many invited and contributed talks or posters at the conference showed new results directly related to these three major developments.Lists of International Advisory Committee (listed by facility), Scientific Programme Committee (listed by facility), Local Organising Committee (listed by facility) are available in this PDF

High-efficiency X-ray emission spectroscopy of cold-compressed Fe2O3 and laser-heated pressurized FeCO3 using a von Hamos ´ spectrometer

X-ray spectroscopy of iron-bearing compounds under high pressure and high temperature is an important tool to understand geological processes in the deep Earth. However, the sample environment using a diamond anvil cell complicates spectroscopic measurements and leads to long data acquisition times. We present a setup for resonant and non-resonant X-ray emission spectroscopy and showcase its capabilities for in situ studies at high pressure and high temperature. Spin-state imaging of laser-heated FeCO3 at 75 GPa via Kβ1,3 emission spectroscopy demonstrates the great potential of this setup with measurement times within seconds for robust spin-state analysis results. The results of Kβ1,3 emission spectroscopy of cold-compressed Fe2O3 reveal a two-step spin transition with the ζ-phase between 57 GPa and 64 GPa, having iron in different spin states at the different iron sites. The phase transition via ζ- to Θ-phase causes a delocalization of the electronic states, which is supported by 1s2p resonant X-ray emission spectroscopy.ISSN:0267-9477ISSN:1364-554

High-efficiency X-ray emission spectroscopy of cold-compressed Fe2_2O3_3 and laser-heated pressurized FeCO3_3 using a von Hámos spectrometer

X-ray spectroscopy of iron-bearing compounds under high pressure and high temperature is an important tool to understand geological processes in the deep Earth. However, the sample environment using a diamond anvil cell complicates spectroscopic measurements and leads to long data acquisition times. We present a setup for resonant and non-resonant X-ray emission spectroscopy and showcase its capabilities for in situ studies at high pressure and high temperature. Spin-state imaging of laser-heated FeCO$_3$ at 75$\,$GPa via Kβ$_{1,3}$ emission spectroscopy demonstrates the great potential of this setup with measurement times within seconds for robust spin-state analysis results. The results of Kβ$_{1,3}$ emission spectroscopy of cold-compressed Fe$_2$O$_3$ reveal a two-step spin transition with the ζ-phase between 57$\,$GPa and 64$\,$GPa, having iron in different spin states at the different iron sites. The phase transition via ζ- to Θ-phase causes a delocalization of the electronic states, which is supported by 1s2p resonant X-ray emission spectroscopy

Ion association in hydrothermal aqueous NaCl solutions: implications for the microscopic structure of supercritical water

Knowledge of the microscopic structure of fluids and changes thereof with pressure and temperature is important for the understanding of chemistry and geochemical processes. In this work we investigate the influence of sodium chloride on the hydrogen-bond network in aqueous solution up to supercritical conditions. A combination of in situ X-ray Raman scattering and ab initio molecular dynamics simulations is used to probe the oxygen K-edge of the alkali halide aqueous solution in order to obtain unique information about the oxygen's local coordination around the ions, e.g. solvation-shell structure and the influence of ion pairing. The measured spectra exhibit systematic temperature dependent changes, which are entirely reproduced by calculations on the basis of structural snapshots obtained via ab initio molecular dynamics simulations. Analysis of the simulated trajectories allowed us to extract detailed structural information. This combined analysis reveals a net destabilizing effect of the dissolved ions which is reduced with rising temperature. The observed increased formation of contact ion pairs and occurrence of larger polyatomic clusters at higher temperatures can be identified as a driving force behind the increasing structural similarity between the salt solution and pure water at elevated temperatures and pressures with drawback on the role of hydrogen bonding in the hot fluid. We discuss our findings in view of recent results on hot NaOH and HCl aqueous fluids and emphasize the importance of ion pairing in the interpretation of the microscopic structure of water

Pressure driven spin transition in siderite and magnesiosiderite single crystals

Iron-bearing carbonates are candidate phases for carbon storage in the deep Earth and may play an important role for the Earth’s carbon cycle. To elucidate the properties of carbonates at conditions of the deep Earth, we investigated the pressure driven magnetic high spin to low spin transition of synthetic siderite FeCO$_3$ and magnesiosiderite (Mg$_{0.74}$Fe$_{0.26}$)CO$_3$ single crystals for pressures up to 57 GPa using diamond anvil cells and x-ray Raman scattering spectroscopy to directly probe the iron 3d electron configuration. An extremely sharp transition for siderite single crystal occurs at a notably low pressure of 40.4 ± 0.1 GPa with a transition width of 0.7 GPa when using the very soft pressure medium helium. In contrast, we observe a broadening of the transition width to 4.4 GPa for siderite with a surprising additional shift of the transition pressure to 44.3 ± 0.4 GPa when argon is used as pressure medium. The difference is assigned to larger pressure gradients in case of argon. For magnesiosiderite loaded with argon, the transition occurs at 44.8 ± 0.8 GPa showing similar width as siderite. Hence, no compositional effect on the spin transition pressure is observed. The spectra measured within the spin crossover regime indicate coexistence of regions of pure high- and low-spin configuration within the single crystal

Reflective imaging, on-axis laser heating and radiospectrometry of samples in diamond anvil cells with a parabolic mirror

We describe the use of a silver-coated 90∘ parabolic mirror of 33 mm focal length as objective for imaging, on-axis laser heating and radiospectrometric temperature measurements of a sample compressed in a diamond anvil cell in a laser heating system. There, spatial resolution and imaging quality of the parabolic mirror are similar to the one of a 10× objective. The temperature measurements between 500 and 900 nm are essentially free from chromatic aberration. The parabolic mirror was also perforated with a 220-μm hole, allowing for on-axis imaging, laser heating and incidence of X-rays simultaneously at synchrotron facilities. The parabolic mirror is thus a well-suited alternative to existing refractive and reflective objectives in laboratory and synchrotron laser heating systems.ISSN:0895-7959ISSN:1477-229

Combining X-ray Kβ1,3β_{1,3}, valence-to-core, and X-ray Raman spectroscopy for studying Earth materials at high pressure and temperature: the case of siderite

X-ray emission and x-ray Raman scattering spectroscopy are powerful tools to investigate thelocal electronic and atomic structure of high and low Z elements in-situ. Notably, these methodscan be applied for in-situ spectroscopy at high pressure and high temperature using resistively orlaser-heated diamond anvil cells in order to achieve thermodynamic conditions which are presentin the Earth’s interior. We developed a setup for combined x-ray emission and x-ray Raman scatteringstudies at beamline P01 of PETRA III using a portable wavelength-dispersive von Hamosspectrometer together with the permanently installed multiple-analyzer Johann-type spectrometer.The capabilities of this setup discussed through the investigation of are exemplified by investigatingthe iron spin crossover of siderite FeCO$_3$ up to 49.3GPa by measuring the Fe M$_{2,3}$-edgeand Fe Kβ$_{1,3}$ emission line simultaneously. With this setup, the Fe valence-to-core emission canbe detected simultaneously with the Kβ$_{1,3}$ emission line providing complementary information onthe sample’s electronic structure. By implementing a laser-heating device, we demonstrate thestrength 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 applicationin geoscience that are accessible with the Johann-type XRS spectrometer. This setup providesa unique combination to gain new insights of the spin transition and compression mechanismsof Earth’s mantle materials of importance for comprehension of the macroscopic physical andchemical properties of the Earth’s interior

Structural and electron spin state changes in an x-ray heated iron carbonate system at the Earth's lower mantle pressures

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 FeCO$_3$ sample at a pressure of 51 GPa with up to melting temperatures. We collected spin state sensitive Fe Kβ$_{1,3}$ 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 Fe$_4$C$_3$O$_{12}$ 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

Structural and electron spin state changes in an x-ray heated iron carbonate system at the Earth's lower mantle pressures

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 Kβ1,3 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.ISSN:2643-156

A von Hámos spectrometer for diamond anvil cell experiments at the High Energy Density Instrument of the European X-ray Free-Electron Laser

A von Hámos spectrometer has been implemented in the vacuum interaction chamber 1 of the High Energy Density instrument at the European X-ray Free-Electron Laser facility. This setup is dedicated, but not necessarily limited, to X-ray spectroscopy measurements of samples exposed to static compression using a diamond anvil cell. Si and Ge analyser crystals with different orientations are available for this setup, covering the hard X-ray energy regime with a sub-eV energy resolution. The setup was commissioned by measuring various emission spectra of free-standing metal foils and oxide samples in the energy range between 6 and 11 keV as well as low momentum-transfer inelastic X-ray scattering from a diamond sample. Its capabilities to study samples at extreme pressures and temperatures have been demonstrated by measuring the electronic spin-state changes of (Fe₀.₅Mg₀.₅)O, contained in a diamond anvil cell and pressurized to 100 GPa, via monitoring the Fe Kβ fluorescence with a set of four Si(531) analyser crystals at close to melting temperatures. The efficiency and signal-to-noise ratio of the spectrometer enables valence-to-core emission signals to be studied and single pulse X-ray emission from samples in a diamond anvil cell to be measured, opening new perspectives for spectroscopy in extreme conditions research.ISSN:0909-0495ISSN:1600-577