Fe-bearing carbonates are increasingly recognized as key phases for iron and carbon storage in Earth’s deep interior, yet their physical properties at high pressure remain poorly constrained, particularly for compositionally complex and structurally disordered systems. In this study, we investigate the high-pressure behavior of ordered and disordered ankerite, Ca(Mg₁₋ₓFeₓ)(CO₃)₂ (0 ≤ x ≤ 0.7), to assess the influence of cation ordering on structural evolution, elastic properties, and Fe spin behavior[1,2]. The present work investigates the high-pressure (HP) behaviour of ankerite, Ca(Mg1-xFex)(CO3)2 (x=0.4, 0.7), crystallizing in the R-3 space group, and disordered ankerite with R-3c symmetry. Cation ordering and disordering influence on the physical properties and phase evolution of Fe-dolomite and ankerite [1,2], with important implications for their elastic behaviour, that might help in partially explaining the observed seismic anisotropic anomalies in the mantle wedge [3] as well as contributing in the carbonate’s detection in the inner Earth [4]. Particular attention is given to comparisions with the single carbonate magnesiosiderite, focusing on the Fe spin behavior at high pressure. The analysed P conditions reach 80 GPa, higher than the range typical of the Fe spin crossover in single carbonate magnesiosiderite, i.e., ~43 GPa at room temperatures [5][6]. The results obtained in this work confirm that neither ordered nor disordered ankerite undergo a high-spin to low-spin transition up to 80 GPa, independently on the Fe content. The project was partially funded by the ‘’BMBF-Verbundprojekt 05K2019-Nanoextrem2” and “DFG core facility for high pressure research” (2018) and “SIMP Research Grant in Crystal ‐ chemistry, in memory of Prof. Fiorenzo Mazzi” (2022). References:[1] Zucchini A et al. (2014) Phys Chem Miner 41(10):783-793[2] Zucchini A et al. (2017) Eur J Mineral 29:227-238[3] Liu X and Zhao D (2017) Geophys J Int 210:1410-1431[4] Chariton S et al (2020) Am Miner 105(3):325-332,[5] Cerantola V et al. (2017) Nat Commun 8:15960[6] Liu J et al. (2014) Am Mineral 99:84-93

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 H 2 O 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.

Owing to the availability of bright X-rays sources such as the ESRF-EBS, inelastic X-ray scattering of samples contained in complex sample environments, including high pressure devices, has become feasible. Compared to well-established characterization techniques such as X-ray diffraction or X-ray absorption fine structure spectroscopy, inelastic X-ray scattering of samples under extreme conditions is a relatively novel probe. However, unique information about the electronic, magnetic, and local atomic structure is accessible with inelastic X-ray scattering. Here, capabilities of beamline ID20 of the ESRF in the field of high pressure inelastic X-ray scattering are presented and some recent activities are reviewed.

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.

Fast and efficient (resonant) X-ray emission spectroscopy setup for the electronic structure at lower mantle conditions: high spin in laser-heated FeCO 3 and a two-step spin transition in pressurized Fe 2 O 3 with increasing valence to core intensity.

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 K β 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.

We present a setup exploiting a von Hámos spectrometer in order to study (resonant) X-ray emission of matter exposed to high pressure. The capabilities of this setup are demonstrated for the case of FeO at pressures between 13 GPa and 75 GPa. The setup provides high-quality K β 1,3 X-ray emission spectra at high pressures for iron spin state analysis within minutes and iron valence-to-core spectra in less than one hour. Resonant X-ray emission maps can be obtained on a timescale of one hour with 1.0 eV and in approximately 3 hours with 0.2 eV incident energy resolution. Both K α and K β emission can be utilized to gain L-edge and M-edge-like information, respectively, with the option of measuring both simultaneously. The spin state results on FeO between 13 GPa and 75 GPa are in accordance with recent literature. The structural distortion is reflected in both, valence-to-core spectra and resonant X-ray emission maps, which showcase the great potential of the presented setup. The achieved data acquisition times are promising to couple pressure with temperature by laser heating.

Iron-bearing carbonates play an important role in Earth's carbon cycle. Owing to their stability at mantle conditions, recently discovered iron carbonates with tetrahedrally coordinated carbon atoms are candidates for carbon storage in the deep Earth. The carbonates' iron oxidation and spin state at extreme pressure and temperature conditions contribute to the redox conditions and element partitioning in the deep mantle. By laser heating FeCO3 at pressures of about 83 GPa, Fe43+C3O12 and Fe22+Fe23+C4O13 were synthesized and then investigated by x-ray emission spectroscopy to elucidate their spin state, both in situ and temperature quenched. Our experimental results show both phases in a high-spin state at all pressures and over the entire temperature range investigated, i.e., up to 3000 K. The spin state is conserved after temperature quenching. A formation path is favored where Fe43+C3O12 forms first and then reacts to Fe22+Fe23+C4O13, most likely accompanied by the formation of oxides. Density functional theory calculations of Fe22+Fe23+C4O13 at 80 GPa confirm the experimental findings with both ferric and ferrous iron in high-spin state with antiferromagnetic order at 80 GPa. As the intercrystalline cation partitioning between the Fe-bearing carbonates and the surrounding perovskite and ferropericlase depends on the spin state of the iron, an understanding of the redox conditions prevalent in subducted slab regions in the lower mantle has to take the latter into account. Especially, Fe22+Fe23+C4O13 may play a key role in subducted material in the lower mantle, potentially with a similar role as silicate perovskite.

The determination of the electronic structure of iron-bearing compounds at high pressure and high temperature (HPHT) conditions is of crucial importance for the understanding of the Earth’s interior and planetary matter. Information on their electronic structure can be obtained by X-ray emission spectroscopy (XES) measurements, where the iron’s Kβ1,3 emission provides information about the spin state and the valence-to-core region focusses on the coordination chemistry around the iron and its electronic state. Furthermore, resonant XES (RXES) at the iron’s K-edge reveals even more detailed information about the electronic structure [1]. We present a setup to investigate the electronic structure of iron-bearing compounds in situ at HPHT conditions using XES and RXES. The HPHT conditions are accomplished by diamond anvil cells (DACs) in combination with a portable double-sided Yb:YAG-laser heating setup [2]. The spectroscopy setup contains a wavelength dispersive von Hamos spectrometer in combination with a Pilatus 100K area detector [3]. This setup provides a full Kβ1,3 emission spectrum including valence-to-core emission in a single shot fashion. In combination with a dedicated sample preparation and use of highly intense synchrotron radiation of beamline P01 at PETRA III, the duration of the measurements is shortened to an extend that in situ XES, including valence-to-core, as well as in situ spin state imaging becomes feasible. The use of miniature diamonds [4] enables RXES measurements at the Fe-K edge. By using different analyzer crystals for the von Hamos spectrometer, simultaneous Kα and Kβ detection are feasible, which provides L-edge and M-edge like information. The presented sample is siderite (FeCO3), which is in focus of recent research as it is a candidate for the carbon storage in the deep Earth. Siderite exhibits a complex chemistry at pressures above 50 GPa and temperatures above 1400 K resulting in the formation of carbonates featuring tetrahedrally coordinated CO4-groups instead of the typical triangular-planar CO3-coordination. These carbonates are well understood on a structural level but information on their electronic structure is scarce [5-7]. We present information on the sample’s spin state at in situ conditions of about 75 GPa and 2000 K XES Kβ1,3 imaging as well as RXES measurements for low and high pressure siderite at ambient temperature conditions for Kα and Kβ emission. [1] M. L. Baker et al., Coordination Chemistry Reviews 345, 182 (2017) [2] G. Spiekermann et al., Journal of Synchroton Radiation, 27, 414 (2020) [3] C. Weis et al., Journal of Analytical Atomic Spectroscopy 34, 384 (2019) [4] S. Petitgirard et al., J. Synchrotron Rad. , 24, 276 (2017) [5] J. Liu et al., Scientific Reports, 5, 7640 (2015) [6] M. Merlini et al., American Mineralogist, 100, 2001, (2015) [7] V. Cerantola et al., Nature Communications 8, 15960 (2017)

The understanding of the microstructure of associated liquids promoted by hydrogen-bonding and constrained by steric hindrance is highly relevant in chemistry, physics, biology and for many aspects of daily life. In this study we use a combination of X-ray diffraction, dielectric spectroscopy and molecular dynamics simulations to reveal temperature induced changes in the microstructure of different octanol isomers, i.e., linear 1-octanol and branched 2-, 3- and 4-octanol. In all octanols, the hydroxyl groups form the basis of chain-, cyclic- or loop-like bonded structures that are separated by outwardly directed alkyl chains. This clustering is analyzed through the scattering pre-peaks observed from X-ray scattering and simulations. The charge ordering which pilots OH aggregation can be linked to the strength of the Debye process observed in dielectric spectroscopy. Interestingly, all methods used here converge to the same interpretation: as one moves from 1-octanol to the branched octanols, the cluster structure evolves from loose large aggregates to a larger number of smaller, tighter aggregates. All alcohols exhibit a peculiar temperature dependence of both the pre-peak and Debye process, which can be understood as a change in microstructure promoted by chain association with increased chain length possibly assisted by ring-opening effects. All these results tend to support the intuitive picture of the entropic constraint provided by branching through the alkyl tails and highlight its capital entropic role in supramolecular assembly.

We describe the use of a silver-coated 90 degrees 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 10x objective. The temperature measurements between 500 and 900 nm are essentially free from chromatic aberration. The parabolic mirror was also perforated with a 220-mu m 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.

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.

Combining experimental results obtained with X-ray scattering and field-gradient nuclear magnetic resonance (NMR) and an assessment of new and previous dielectric and rheology data, our study focuses on the molecular weight (M-w) evolution of local structure and dynamics in a homologous series of covalently bonded ionic liquids. Performed on a family of electrolytes with a tailored degree of ionic decoupling, this study reveals the differences between monomeric and oligomeric melts with respect to their structural organization, mass and charge transport, and molecular diffusion. Our study demonstrates that for the monomeric compound, the broadband conductivity and mechanical spectra reflect the same underlying distribution of activation barriers and that the Random Barrier Model describes fairly well both the ionic and structural relaxation processes in these materials. Moreover, the oligomers with chains comprising ten segments only exhibit both structural and dynamical fingerprints of a genuine polymer. A comparison of conductivity levels estimated using the self-diffusion coefficients probed via NMR and those probed directly with dielectric spectroscopy reveals the emerging of ion correlations which are affecting the macroscopic charge transport in these materials in a chain-length dependent manner.

Iron is the most abundant transition metal in Earth minerals such as carbonates and silicates. When exposed to the high pressures and high temperatures that are expected in the Earth’s mantle their electronic structure, e.g. the spin state of iron, can change. Both, Fe and Fe species in such minerals are in the high spin electronic state at ambient conditions and may undergo transitions from high spin to low spin state with increasing pressure as observed for e.g. siderite (FeCO3), magnesiosiderite ((Mg,Fe)CO3), and bridgmanite ((Fe,Mg)SiO3). In the case of the Fe-bearing magnesium silicate perovskite, recently named as bridgmanite, the Fe spin transition is complicated by the crystal chemistry, because Fe may occupy the A and B-site of the lattice and the Fe oxidation state may vary. The high spin to low spin transition was first observed using Kβ x-ray emission (XES) showing a gradual change of the iron’s high spin and low spin fractions in the 30-70 GPa range and a sharp transition to the low spin state at 120 GPa [1]. Originally the gradual transition was assigned to the Fe on the Bsite and the sharp one to that of Fe on the A-site [1,2]. Fe on the A site is at all mantle pressures in the high spin state but due to diffusion from the A-site and oxidation of Fe the Fe content on B-site increases and is almost never negligible. [3,4]. This assignment above was challenged by later Mössbauer measurements that suggest the gradual transition [3] over a large pressure range to be due to the formation of Fe with intermediate spin state on the A-site, based on the appearance of a doublet with unusually high quadrupole splitting above 30 GPa [5]. At 120 GPa the Fe on the A-site converts to the low-spin state [6] consistent with earlier observations XES [1]. Despite those many studies on the transition in bridgmanite, the controversy still lingers on, as documented by latest review articles [2,4,7]. Here, our recent results on the spin-state of ferrous (Fe) and ferric (Fe) iron in bridgmanite will be presented and discussed in in context to the results obtained by Badro et al. [1]. Preliminary analysis of the ferrous iron data implies that the results there [1] cannot be explained by a combination of our ferrous data and results obtained by Liu et al. [8] on ferric iron. In order to study the course of the spin transition and corresponding changes in local coordination we combine complementary x-ray spectroscopies, i.e. x-ray absorption (XAS) at the iron Kedge, iron Kβ and valence-to-core (vtc) x-ray emission (XES). Tracking changes in the coordination state and oxidation state we evaluate the Fe K-edge pre-edge feature position and intensity [9] from XAS. The XES experiments were performed using an energy dispersive von Hamos type spectrometer in combination with a Pilatus area detector for simultaneous acquisition of Fe Kβ and vtc XES [10] together with XAS measurements. In previous experiments our group demonstrated a good agreement between x-ray emission and x-ray absorption like analysis of Fe Land M-edge x-ray Raman scattering (XRS) [11]. Consequently, the combination of these methods will help to further constrain the spin state, local coordination and oxidation state of iron in ferrous and ferric bridgmanite at pressure aiming to solve the controversy on the iron’s spin state in bridgmanite.

The high spin to low spin transition of siderite is studied by simultaneous X-ray emission and X-ray Raman scattering spectroscopy.

Over the last decade, great efforts have been undertaken in science and industry to provide WC-Co feedstock with nano-sized WC particles that significantly improves tribo-mechanical coating properties. For tribologically stressed surfaces, superior surface characteristics can be achieved by applying tailored surfaces, using novel technologies in the field of production engineering such as High-Feed Milling (HFM). For the first time, textured surface patterns were produced onto HVOF sprayed WC-Co coatings with nanosized WC particles by implementing a HFM post process. In dependence to two different textures resulting from the HFM, the microstructural characteristics of the produced surfaces are analyzed. Confocal microscopy revealed the machinability of textured patterns onto a HVOF-sprayed WC-12Co hard coating, which comprise of nano-sized WC particles, by means of HFM technology. X-ray diffraction analyses confirmed the insertion of macro- and micro-scale residual stresses. The experiments showed a significant insertion of compressive residual stresses transverse to the feed direction, whereas the insertion of compresses residual stresses with its feed direction being less pronounced. It was found that the HFM post process leads to a refinement of the WC crystallite size and a distinct increase of its internal strain, which both can be attributed to plastic deformations during HFM.

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.