BM23 is the general‐purpose EXAFS bending‐magnet beamline at the ESRF, replacing the former BM29 beamline in the framework of the ESRF upgrade. Its mission is to serve the whole XAS user community by ...providing access to a basic service in addition to the many specialized instruments available at the ESRF. BM23 offers high signal‐to‐noise ratio EXAFS in a large energy range (5–75 keV), continuous energy scanning for quick‐EXAFS on the second timescale and a micro‐XAS station delivering a spot size of 4 µm × 4 µm FWHM. It is a user‐friendly facility featuring a high degree of automation, online EXAFS data reduction and a flexible sample environment.
The European Synchrotron Radiation Facility has recently made available to the user community a facility totally dedicated to Time‐resolved and Extreme‐conditions X‐ray Absorption Spectroscopy – ...TEXAS. Based on an upgrade of the former energy‐dispersive XAS beamline ID24, it provides a unique experimental tool combining unprecedented brilliance (up to 1014 photons s−1 on a 4 µm × 4 µm FWHM spot) and detection speed for a full EXAFS spectrum (100 ps per spectrum). The science mission includes studies of processes down to the nanosecond timescale, and investigations of matter at extreme pressure (500 GPa), temperature (10000 K) and magnetic field (30 T). The core activities of the beamline are centered on new experiments dedicated to the investigation of extreme states of matter that can be maintained only for very short periods of time. Here the infrastructure, optical scheme, detection systems and sample environments used to enable the mission‐critical performance are described, and examples of first results on the investigation of the electronic and local structure in melts at pressure and temperature conditions relevant to the Earth's interior and in laser‐shocked matter are given.
Abstract
The discovery of superconductivity above 250 K at high pressure in LaH
10
and the prediction of overcoming the room temperature threshold for superconductivity in YH
10
urge for a better ...understanding of hydrogen interaction mechanisms with the heavy atom sublattice in metal hydrides under high pressure at the atomic scale. Here we use locally sensitive X-ray absorption fine structure spectroscopy (XAFS) to get insight into the nature of phase transitions and the rearrangements of local electronic and crystal structure in archetypal metal hydride YH
3
under pressure up to 180 GPa. The combination of the experimental methods allowed us to implement a multiscale length study of YH
3
: XAFS (short-range), Raman scattering (medium-range) and XRD (long-range). XANES data evidence a strong effect of hydrogen on the density of 4
d
yttrium states that increases with pressure and EXAFS data evidence a strong anharmonicity, manifested as yttrium atom vibrations in a double-well potential.
Solid krypton (Kr) undergoes a pressure-induced martensitic phase transition from a face-centered cubic (fcc) to a hexagonal close-packed (hcp) structure. These two phases coexist in a very wide ...pressure domain inducing important modifications of the bulk properties of the resulting mixed phase system. Here, we report a detailed in situ x-ray diffraction and absorption study of the influence of the fcc-hcp phase transition on the compression behavior of solid krypton in an extended pressure domain up to 140 GPa. The onset of the hcp-fcc transformation was observed in this study at around 2.7 GPa and the coexistence of these two phases up to 140 GPa, the maximum investigated pressure. The appearance of the hcp phase is also evidenced by the pressure-induced broadening and splitting of the first peak in the XANES spectra. We demonstrate that the transition is driven by a continuous nucleation and intergrowth of nanometric hcp stacking faults that evolve in the fcc phase. These hcp stacking faults are unaffected by high-temperature annealing, suggesting that plastic deformation is not at their origin. The apparent small Gibbs free-energy differences between the two structures that decrease upon compression may explain the nucleation of hcp stacking faults and the large coexistence domain of fcc and hcp krypton. We observe a clear anomaly in the equation of state of the fcc solid at ∼20 GPa when the proportion of the hcp form reaches ∼20%. We demonstrate that this anomaly is related to the difference in stiffness between the fcc and hcp phases and propose two distinct equation of states for the low and high-pressure regimes.
Noble gases are important geochemical tracers allowing reconstructing global volatile cycles in Earth's reservoirs. To constrain these fundamental processes, precise data on their partitioning ...behavior at deep Earth conditions are needed. Such data are only available at moderate pressures up to 25 GPa due to experimental challenges. We have investigated the possibility of noble gas storage in the Earth's lower mantle up to 115 GPa. We studied the incorporation of krypton in the second most abundant lower mantle mineral (Mg1-x,Fex)O (ferropericlase) as well as in liquid metal-alloys by performing experiments up to 115 GPa and 3700 K using the laser-heated diamond anvil cell coupled to post-mortem EMPA analysis and X-ray absorption spectroscopy. The results reveal that, at these extreme conditions, up to 3 wt.% of krypton can be stored in (Mg1-x,Fex)O and 3000 ppm in the Fe-rich liquid metal. For both phases the storage capacities increase with pressure (between 40 GPa and 60 GPa) at a constant high temperature of 2300 K. Fpc has never been considered as a NG host, despite being the second most abundant mineral in the Earth's LM. Using recent accurate compressibility data, we demonstrate that a substitution of krypton into the anion site of (Mg1-x,Fex)O in form of neutral oxygen Schottky defects at diluted lower mantle conditions is possible. This noble gas incorporation mechanism is in agreement with a previous study on bridgmanite. We show that (Mg1-x,Fex)O exhibits higher noble gas storage capacities than bridgmanite through the lower mantle using lattice strain modeling and including experimental solubility and thermoelastic data for neon, argon, krypton and xenon. We also demonstrate that both phases exhibit the highest solubilities for argon and krypton. We used the solubility data from lattice strain modeling to predict noble gas abundances stored in the solid lower mantle after magma ocean crystallization. The modeled abundances show apparent similarities with estimates for the deep noble gas reservoir that are based on either 3He abundances in ocean island basalts or radiogenic 40Ar abundances in the bulk Earth. This strongly indicates that the crystalline lower mantle may play an important role as deep noble gas storage reservoir. We propose, based on considerations on noble gas replenishment from the lower mantle to the atmosphere, that the lower mantle can only contribute to a small fraction of the present-day atmospheric noble gases. This suggests that the lower mantle is an un-degassed reservoir.
•Krypton storage capacities of (Mg,Fe)O and metal alloys up to 115 GPa and 3700 K.•Storage capacities of lower mantle minerals are greater than those of metallic melts.•Zero-charged krypton is incorporated in neutral oxygen defects of (Mg,Fe)O.•The lower mantle could be a reservoir for noble gases through geologic times.
•X-ray absorption spectroscopy coupled to the diamond anvil cell technology is a powerful tool to investigate matter at high pressure.•Several X-ray absorption spectroscopy beamlines at synchrotrons ...around the world are equipped to offer XAS and XMCD spectroscopy for high pressure studies.•X-ray magnetic circular dichroism has been employed to investigate pressure induced suppression of ferromagnetism in Fe, Co and Ni.•The availability of high quality data at extreme conditions is very useful to validate existing theoretical models.
The study of the properties of matter under extreme conditions allows reproducing the physical conditions of inaccessible regions of the earth and planets, encountering a geophysical interest. Also it addresses fundamental questions concerning the stability of the crystallographic structure, the magnetic order and the electronic structure thus giving an insight into their own appearance. In this review we illustrate how X-ray absorption spectroscopies, coupled to diamond anvil cell techniques, can be successfully employed at this purpose. As an example, we describe recent advances in the investigation of the ferromagnetic transition metals under high pressure.
Isotopic signatures of heavy noble gases in the Earth's mantle contain a major component recycled by subduction. The experimental and field studies reported in the literature show increasing evidence ...that serpentine minerals can hold large quantities of noble gases, potentially serving as their primary vectors to depth. However, at present, their retention mechanism in these minerals is not fully understood. Additionally, noble gas solubilities from field and experimental studies show large differences in terms of elemental concentrations. Here, we performed crystal chemical modeling to evaluate the incorporation mechanism of noble gases and their solubilities in serpentine minerals along subduction zone geotherms. To this end, we determined the thermal equation of state of xenon using in situ X-ray diffraction and absorption up to 60 GPa and 728 K. In this range, the xenon equation of state is well-adjusted using the Mie-Grüneisen-Debye formalism with relevant fitting parameters. We show that the experimentally observed solubility trend, which follows the order Ne < He < Ar < Kr < Xe, can be explained by the incorporation of noble gases at two distinct crystallographic sites. The light noble gases He and Ne are most likely retained at the van der Waals hydrogen-oxygen bond position between the layers, while the heavy and larger noble gases enter the voids between the six-membered SiO4 rings. It should be noted that octahedral sites can potentially host xenon, but cannot accommodate argon and krypton. Indeed, this would require unrealistic flexibility of the crystal lattice. Our models extended to mantle wedge conditions predict decreasing solubilities, particularly for light noble gases, in agreement with observations from natural samples. Compared to the noble gas concentrations determined experimentally in serpentine, natural concentrations are much higher and very variable. Our solubility model confirms that equilibrium processes cannot explain these observations. We therefore suggest that the high and variable noble gas concentrations found in natural samples must be due to hybrid hydration processes in ultramafic rocks that involve different degrees of water activities.
When high pressure is applied to Ce-Al metallic glasses, their disordered atomic structure exhibits some unusual properties like polyamorphism or transformation into a crystalline phase. In this ...work, we probe the atomic arrangement of Ce55Al45 and Ce75Al25 glasses by X-ray absorption spectroscopy and X-ray diffraction in the pressure range of 0–30 GPa. The pressure-dependent parameters of local environment of cerium atoms are evaluated by extended X-ray absorption fine structure (EXAFS) fitting. We demonstrate that due to compositional dependence of stiffness of Ce-Al pairs, densification of Ce55Al45 is accompanied by an increase of atomic size mismatch between Ce and Al stabilizing the amorphous phase, while a decrease of the mismatch is observed in Ce75Al25 alloy which eventually leads to its devitrification at 25 GPa.
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•Ce-Ce pairs are nearly equally stiff in Ce55Al45 and Ce75Al25 metallic glasses.•Ce-Al pairs are significantly more stiff in Ce75Al25 than in Ce55Al45.•On compression, Al/Ce size mismatch decreases in Ce75Al25 and increases in Ce55Al45.•Devitrification of Ce75Al25 results from a topological instability of the glass.
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