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Using the density functional theory, we study the structural and lattice dynamical properties of europium sesquioxide ($Eu_{2}O_{3}$) in the cubic, trigonal, and monoclinic phases. The obtained lattice parameters and energies of the Raman modes show a good agreement with the available experimental data. The Eu-partial phonon density of states calculated for the cubic structure is compared with the nuclear inelastic scattering data obtained from a 20 nm thick $Eu_{2}O_{3}$ film deposited on a YSZ substrate. A small shift of the experimental spectrum to higher energies results from a compressive strain induced by the substrate. On the basis of lattice and phonon properties, we analyze the mechanisms of structural transitions between different phases of $Eu_{2}O_{3}$.

In order to calculate the thermodynamic properties for recently discovered high-pressure mixed valence iron-oxides in the system Fe-Mg-O, information on the equation of state of precursor inverse spinel phases along the magnetite-magnesioferrite join is needed. The existing equation of state data, particularly for magnesioferrite, are in poor agreement and no data exist for intermediate compositions. In this study, the compressibility of nearly pure magnesioferrite as well as of an intermediate \({{\text{M}\text{g}}_{0.5}\text{F}\text{e}}_{0.5}^{2+}{\text{F}\text{e}}_{2}^{3+}{O}_{4}\) sample have been investigated for the first time up to approximately 13 and 19 GPa respectively, using single crystal X-ray diffraction in a diamond anvil cell. Samples were produced in high-pressure experiments to promote a high level of cation ordering, with resulting inversion parameters of x = 0.892(2) and x = 0.98(3) for the endmember and intermediate composition, respectively. The room pressure unit cell volumes, V0, and bulk moduli, KT0, could be adequately constrained using a 2nd order Brich-Murnaghan equation of state, which yield V0 =588.97 (8) Å3 and KT0 = 178.4(5) GPa for magnesioferrite and V0 = 590.21(5) Å3 and KT0 = 188.0(6) GPa for the intermediate composition. As magnetite has KT0 = 180(1) GPa (Gatta et al., 2007), this means the variation in KT0 across the magnetite-magnesioferrite solid solution is significantly non-linear, in contrast to several other Fe-Mg spinels. The larger incompressibility of the intermediate composition compared to the two endmembers may be a peculiarity of the magnetite-magnesioferrite solid solution caused by an interruption of Fe2+-Fe3+ electron hopping by Mg cations substituting in the octahedral site.

Electronic states of iron in the lower mantle's dominant mineral, (Mg,Fe,Al)(Fe,Al,Si)O3 bridgmanite, control physical properties of the mantle including density, elasticity, and electrical and thermal conductivity. However, the determination of electronic states of iron has been controversial, in part due to different interpretations of Mössbauer spectroscopy results used to identify spin state, valence state, and site occupancy of iron. We applied energy-domain Mössbauer spectroscopy to a set of four bridgmanite samples spanning a wide range of compositions: 10–50% Fe/total cations, 0–25% Al/total cations, 12–100% Fe3+/total Fe. Measurements performed in the diamond-anvil cell at pressures up to 76 GPa below and above the high to low spin transition in Fe3+ provide a Mössbauer reference library for bridgmanite and demonstrate the effects of pressure and composition on electronic states of iron. Results indicate that although the spin transition in Fe3+ in the bridgmanite B-site occurs as predicted, it does not strongly affect the observed quadrupole splitting of 1.4 mm/s, and only decreases center shift for this site to 0 mm/s at ~70 GPa. Thus center shift can easily distinguish Fe3+ from Fe2+ at high pressure, which exhibits two distinct Mössbauer sites with center shift ~1 mm/s and quadrupole splitting 2.4–3.1 and 3.9 mm/s at ~70 GPa. Correct quantification of Fe3+/total Fe in bridgmanite is required to constrain the effects of composition and redox states in experimental measurements of seismic properties of bridgmanite. In Fe-rich, mixed-valence bridgmanite at deep-mantle-relevant pressures, up to ~20% of the Fe may be a Fe2.5+ charge transfer component, which should enhance electrical and thermal conductivity in Fe-rich heterogeneities at the base of Earth's mantle.

International audience; Spin crossover complexes are among the most studied classes of molecular switches and have attracted considerable attention for their potential technological use as active units in multifunctional devices. A fundamental step toward their practical implementation is the integration in macroscopic devices adopting hybrid vertical architectures. First, the physical properties of technological interest shown by these materials in the bulk phase have to be retained once they are deposited on a solid surface. Herein, we describe the study of a hybrid molecular inorganic junction embedding the spin crossover complex [Fe(qnal)2] (qnal = quinoline-naphthaldehyde) as an active switchable thin film sandwiched within energy-optimized metallic electrodes. In these junctions, developed and characterized with the support of state of the art techniques including synchrotron Mössbauer source (SMS) spectroscopy and focused-ion beam scanning transmission electron microscopy, we observed that the spin state conversion of the Fe(II)-based spin crossover film is associated with a transition from a space charge-limited current (SCLC) transport mechanism with shallow traps to a SCLC mechanism characterized by the presence of an exponential distribution of traps concomitant with the spin transition temperature.

Thanks to the physical strength of diamonds and their relatively unreactive chemical nature, their mineral inclusions may remain exceptionally preserved from alteration processes and chemical exchanges with surrounding minerals, fluids and/or melts following diamond formation. Cr-bearing spinels are relatively common inclusions found in peridotitic diamonds and important oxybarometers providing information about the oxygen fugacity (fO2) of their source mantle rocks. Here, we investigated a magnesiochromite–olivine touching pair in a diamond from the Udachnaya kimberlite (Siberia) by in situ single-crystal X-ray diffraction and energy-domain synchrotron Mössbauer spectroscopy, aiming to constrain the physical–chemical conditions of diamond formation and to explore the redox state of this portion of the Siberian craton when the diamond was formed. The P–T–fO2 entrapment conditions of the inclusion pair, determined by thermo- and oxybarometric analyses, are ∼ 5.7(0.4) GPa and ∼ 1015(50) ∘C (although entrapment at higher T and re-equilibration during subsequent mantle storage are also possible) and fO2 near the enstatite–magnesite–olivine–diamond (EMOD) buffer. The determined fO2 is similar to, or slightly more oxidized than, those of xenoliths from Udachnaya, but whilst the xenoliths last equilibrated with the surrounding mantle just prior to their entrainment in the kimberlite at ∼ 360 Ma, the last equilibration of the inclusion pair is much older, occurring at 3.5–3.1, ∼ 2 or ∼ 1.8 Ga before final encapsulation in its host diamond. Hence, the similarity between xenoliths and inclusion fO2 values indicates that the modern redox state of this portion of the Siberian lithosphere was likely attained relatively early after its formation and may have persisted for billions of years after diamond formation, at least at the local scale. Moreover, the oxygen fugacity determination for the inclusion pair provides direct evidence of diamond formation near the EMOD buffer and is consistent with recent models suggesting relatively oxidized, water-rich CHO fluids as the most likely parents for lithospheric diamonds.

The spatial confinement of atoms at surfaces and interfaces significantly alters the lattice dynamics of thin films, heterostructures and multilayers. Ultrathin films with high dielectric constants (high

Using the density functional theory, we study the structural and lattice dynamical properties of europium sesquioxide (Eu2O3) in the cubic, trigonal, and monoclinic phases. The obtained lattice parameters and energies of the Raman modes show a good agreement with the available experimental data. The Eu-partial phonon density of states calculated for the cubic structure is compared with the nuclear inelastic scattering data obtained from a 20 nm thick Eu2O3 film deposited on a YSZ substrate. A small shift of the experimental spectrum to higher energies results from a compressive strain induced by the substrate. On the basis of lattice and phonon properties, we analyze the mechanisms of structural transitions between different phases of Eu2O3., The phase transitions of rare-earth sesquioxide Eu2O3 are very complicated. Analyzing dynamical properties of this compound for experimentally observed C-, A-, and B-type phases and extracting key symmetry elements common for these phases, we describe transition mechanisms and their sequence. Our DFT first-principles predictions are supported by the nuclear inelastic scattering measurements.

The structure and properties of metal-hydrides at extreme conditions is key to the understanding of hydrogen-storage technologies, high-temperature superconductivity, and the dynamics of planetary cores. Here we investigate the phase relations and magnetic properties of iron hydrides, including two novel FeHx compounds, up to 63 GPa and 1800 K by Synchrotron Mössbauer Source spectroscopy and single-crystal X-ray diffraction. We observe the formation of a novel monoclinic iron hydride phase Fe2H∼3 at 63 GPa and 1000 K, which breaks down to a stoichiometric hexagonal closed packed FeH phase upon decompression below 52 GPa at 300 K. The long-range magnetic order in the two newly-synthetized phases persists to higher pressures compared to the well-known double hexagonal closed packed and face-centered cubic phases of FeH. The formation of magnetic Fe-H phases with high hydrogen concentration may influence the magnetic behavior of planetary metallic cores.

Iron and stony‐iron meteorites form the Widmanstätten pattern during slow cooling. This pattern is composed of several microstructures whose length‐scale, composition and magnetic properties are dependent upon cooling rate. Here we focus on the cloudy zone: a region containing nanoscale tetrataenite islands with exceptional paleomagnetic recording properties. We present a systematic review of how cloudy zone properties vary with cooling rate and proximity to the adjacent tetrataenite rim. X‐ray photoemission electron microscopy is used to compare compositional and magnetization maps of the cloudy zone in the mesosiderites (slow cooling rates), the IAB iron meteorites and the pallasites (intermediate cooling rates), and the IVA iron meteorites (fast cooling rates). The proportions of magnetic phases within the cloudy zone are also characterized using Mössbauer spectroscopy. We present the first observations of the magnetic state of the cloudy zone in the mesosiderites, showing that, for such slow cooling rates, tetrataenite islands grow larger than the multidomain threshold, creating large‐scale regions of uniform magnetization across the cloudy zone that render it unsuitable for paleomagnetic analysis. For the most rapidly cooled IVA meteorites, the time available for Fe‐Ni ordering is insufficient to allow tetrataenite formation, again leading to behavior that is unsuitable for paleomagnetic analysis. The most reliable paleomagnetic remanence is recorded by meteorites with intermediate cooling rates ( urn:x-wiley:ggge:media:ggge22125:ggge22125-math-0001 2–500 °C Myr urn:x-wiley:ggge:media:ggge22125:ggge22125-math-0002) which produces islands that are “just right” in both size and degree of Fe‐Ni order., This work was supported by the European Research Council under the European Union's Seventh Framework Programme (FP/2007‐2013)/ ERC grant agreement numbers 320750 and 312284.

The performance of a liquid-nitrogen-cooled high-heat-load monochromator with a horizontal scattering plane has been analysed, aiming to preserve the high quality of the X-ray beam in the vertical plane for downstream optics. Using finite-element analysis, height profiles of the crystal surface for various heat loads and the corresponding slope errors in the meridional and sagittal planes were calculated. Then the angular distortions of the reflected beam in both meridional and sagittal planes were calculated analytically and also modelled by ray tracing, revealing a good agreement of the two approaches. The results show that with increasing heat load in the crystal the slope errors of the crystal surface reach their smallest values first in the sagittal and then in the meridional plane. For the considered case of interest at a photon energy of 14.412 keV and the Si(111) reflection with a Bragg angle of 7.88°, the angular distortions of the reflected beam in the sagittal plane are an order of magnitude smaller than in the meridional one. Furthermore, they are smaller than the typical angular size of the beam source at the monochromator position. For a high-heat-load monochromator operating in the horizontal scattering plane, the sagittal angular distortions of the reflected beam appear in the vertical plane. Thus, such an instrument perfectly preserves the high quality of the X-ray beam in the vertical plane for downstream optics. Compared with vertical scattering, the throughput of the monochromatic beam with the horizontal scattering plane is reduced by only 3.3% for the new EBS source, instead of 34.3% for the old ESRF-1 machine. This identifies the horizontal-scattering high-heat-load monochromator as a device essentially free of the heat-load effects in the vertical plane and without significant loss in terms of throughput.

Herein, evidence for the long-sought finite hyperfine interaction in the high-pressure hexagonal close-packed $\ensuremath{\epsilon}$-iron is gained through synchrotron radiation perturbed angular correlation spectroscopy. This method yields an energy splitting of $3.5(5)\phantom{\rule{4.pt}{0ex}}\text{neV}$ between the ${m}_{{I}_{\text{e}}}=\ifmmode\pm\else\textpm\fi{}1/2$ and ${m}_{{I}_{\text{e}}}=\ifmmode\pm\else\textpm\fi{}3/2$ nuclear sublevels of the iron-57 $14.412\text{-keV}$ nuclear excited state at $30(1)\phantom{\rule{4.pt}{0ex}}\text{GPa}$ and room temperature. This energy splitting is related to a nuclear quadrupole hyperfine interaction with an electric field gradient of $eq=1.2(2)\ifmmode\times\else\texttimes\fi{}{10}^{16}{\phantom{\rule{0.16em}{0ex}}\mathrm{V}/\mathrm{cm}}^{2}$. However, there is still a possibility that the splitting of the iron-57 nuclear levels is related to a modest magnetic hyperfine interaction of ca. $0.40(5)\phantom{\rule{4.pt}{0ex}}\text{T}$.

α-Sb2O3 (senarmontite), β-Sb2O3 (valentinite), and α-TeO2 (paratellurite) are compounds with pronounced stereochemically active Sb and Te lone pairs. The vibrational and lattice properties of each have been previously studied but often lead to incomplete or unreliable results due to modes being inactive in infrared or Raman spectroscopy. Here, we present a study of the relationship between bonding and lattice dynamics of these compounds. Mossbauer spectroscopy is used to study the structure of Sb in α-Sb2O3 and β-Sb2O3, whereas the vibrational modes of Sb and Te for each oxide are investigated using nuclear inelastic scattering, and further information on O vibrational modes is obtained using inelastic neutron scattering. Additionally, vibrational frequencies obtained by density functional theory (DFT) calculations are compared with experimental results in order to assess the validity of the utilized functional. Good agreement was found between DFT-calculated and experimental density of phonon states with a 7% scaling factor. The Sb-O-Sb wagging mode of α-Sb2O3 whose frequency was not clear in most previous studies is experimentally observed for the first time at ∼340 cm-1. Softer lattice vibrational modes occur in orthorhombic β-Sb2O3 compared to cubic α-Sb2O3, indicating that the antimony bonds are weakened upon transforming from the molecular α phase to the layer-chained β structure. The resulting vibrational entropy increase of 0.45 ± 0.1 kB/Sb2O3 at 880 K accounts for about half of the α-β transition entropy. The comparison of experimental and theoretical approaches presented here provides a detailed picture of the lattice dynamics in these oxides beyond the zone center and shows that the accuracy of DFT is sufficient for future calculations of similar material structures.

Minerals 10(6), 542 (2020). doi:10.3390/min10060542, It is widely accepted that the lower mantle consists of mainly three major minerals—ferropericlase, bridgmanite and calcium silicate perovskite. Ferropericlase ((Mg,Fe)O) is the second most abundant of the three, comprising approximately 16–20 wt% of the lower mantle. The stability of ferropericlase at conditions of the lowermost mantle has been highly investigated, with controversial results. Amongst other reasons, the experimental conditions during laser heating (such as duration and achieved temperature) have been suggested as a possible explanation for the discrepancy. In this study, we investigate the effect of pulsed laser heating on the stability of ferropericlase, with a geochemically relevant composition of Mg$_{0.76}$Fe$_{0.24}$O (Fp24) at pressure conditions corresponding to the upper part of the lower mantle and at a wide temperature range. We report on the decomposition of Fp24 with the formation of a high-pressure (Mg,Fe)$_3$O$_4$ phase with CaTi$_2$O$_4$-type structure, as well as the dissociation of Fp24 into Fe-rich and Mg-rich phases induced by pulsed laser heating. Our results provide further arguments that the chemical composition of the lower mantle is more complex than initially thought, and that the compositional inhomogeneity is not only a characteristic of the lowermost part, but includes depths as shallow as below the transition zone., Published by MDPI, Basel

We explore alternative ways to Mossbauer spectroscopy such as nuclear forward scattering of synchrotron radiation, and synchrotron radiation perturbed angular correlation spectroscopy to reveal the elusive and long-sought hyperfine interactions in e-Fe. We indicate that synchrotron radiation perturbed angular correlation spectroscopy is the most viable method.

Nuclear resonance reflectivity from a [Dy19Gd19] × 20 superlattice has been measured utilizing the 25.652 keV nuclear level of 161Dy. The measured time spectra of nuclear resonance reflectivity make it possible to reveal the variation of the hyperfine magnetic field Bhf on dysprosium nuclei in the temperature range of 4–110 K and to determine the relaxation time of the hyperfine field, using the decay speed-up of the excited state of 161Dy nuclei.

Nanostructured epitaxial [57Fe(1.2 A)/Cr(10.5 A)]30 multilayer with ultrathin Fe layers, demonstrated Kondo-like behavior, has been investigated by means of the nuclear resonance reflectivity at low temperatures (down to 4 K) in magnetic fields up to 4 T. We detected the beginning of the magnetic phase transition at 150 K which correlates with the minimum on the electrical resistivity curve. The determined magnetic hyperfine field distribution P(Bhf) indicates an inhomogeneity of the iron environments. When we apply the very high external magnetic field up to 4 T, it aligns Bhf(i) along the direction of the external field only partially. Also it has been noticed that Bhf(i) orientations depend on the magnetic pre-history.

Nuclear inelastic scattering of synchrotron radiation has been used to determine the phonon density of vibrational states (pDOS) for the high-spin and low-spin phases of the hydrated and dehydrated isomer of the spin crossover polymer [Fe(pyrazine)][Pt(CN)

The densities of phonon states of thin Sn films on InSb substrates are determined during different stages of the $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Sn}$ to $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{Sn}$ phase transition using nuclear inelastic x-ray scattering. The vibrational entropy and internal energy per atom as a function of temperature are obtained by numerical integration of the phonon density of states. The free energy as a function of temperature for the nanoscale samples is compared to the free energy obtained from ab initio calculations of bulk tin in the $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Sn}$ and $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{Sn}$ phase. In thin films this phase transition is governed by the interplay between the vibrational behavior of the film (the phase transition is driven by the vibrational entropy) and the stabilizing influence of the substrate (which depends on the film thickness). This brings a deeper understanding of the role of lattice vibrations in the phase transition of nanoscale Sn.

Self-amplified spontaneous emission (SASE) enables X-ray free-electron lasers (XFELs) to generate hard X-ray pulses of sub-100 fs duration. However, due to the stochastic nature of SASE, the energy spectrum fluctuates from pulse to pulse. Many experiments that employ XFEL radiation require the resolution of the spectrum of each pulse. The work presented here investigates the capacity of a thin strongly bent diamond crystal to resolve the energy spectra of hard X-ray SASE pulses by studying its diffraction properties. Rocking curves of the symmetric C*(440) reflection have been measured for different bending radii. The experimental data match the theoretical modelling based on the Takagi–Taupin equations of dynamical diffraction. A uniform strain gradient has proven to be a valid model of strain deformations in the crystal.

Dalton transactions 48(41), 15625 - 15634 (2019). doi:10.1039/C9DT02139F, Nuclear inelastic scattering of synchrotron radiation has been used to determine the phonon density of vibrational states (pDOS) for the high-spin and low-spin phases of the hydrated and dehydrated isomer of the spin crossover polymer [Fe(pyrazine)][Pt(CN)4]. Density functional theory calculations have been performed for molecular models of the 3D polymeric system. The models contain 15 Fe(II)/Zn(II) centres and allowed the assignment of the observed bands to the corresponding vibrational modes. Thermodynamic parameters like the mean force constant and the vibrational entropy but also sound velocities of the molecular lattices in both spin states have been derived from the pDOS. Modelling of the low-spin and high-spin centres in the environment or matrix of different spins has revealed the enthalpic and entropic components of the intramolecular cooperativity. In contrast to the 1D spin crossover systems (Rackwitz, et al., Phys. Chem. Chem. Phys., 2013, 15, 15450) based on the rigid 1,2,4-triazole derivatives the distortion of the low-spin iron Fe(II) centre by the matrix of high-spin Fe(II) (modelled as Zn(II)) occurs only in two dimensions, defined by the [M(CN)4]2− sheets, rather than concerning all six Fe–N bonds, as in 1D systems. The enthalpic intramolecular cooperativity has been determined to be 15 kJ mol−1 which is lower than that in 1D systems (20–30 kJ mol−1). Yet, the entropic contribution stabilizes the low-spin state in a low-spin matrix, a behaviour which is opposite to what was found for the 1D systems., Published by Soc., London

Polarization selection of the reflected radiation has been employed in M&ouml, ssbauer reflectivity measurements with a synchrotron M&ouml, ssbauer source (SMS). The polarization of resonantly scattered radiation differs from the polarization of an incident wave so the M&ouml, ssbauer reflectivity contains a scattering component with 90&deg, rotated polarization relative to the &pi, polarization of the SMS for some hyperfine transitions. We have shown that the selection of this rotated &pi, &rarr, &sigma, component from total reflectivity gives an unusual angular dependence of reflectivity characterized by a peak near the critical angle of the total external reflection. In the case of collinear antiferromagnetic interlayer ordering, the &ldquo, magnetic&rdquo, maxima on the reflectivity angular curve are formed practically only by radiation with this rotated polarization. The first experiment on M&ouml, ssbauer reflectivity with a selection of the rotated polarization discovers the predicted peak near the critical angle. The measurement of the rotated &pi, polarization component in M&ouml, ssbauer reflectivity spectra excludes the interference with non-resonant electronic scattering and simplifies the spectrum shape near the critical angle allowing for an improved data interpretation in the case of poorly resolved spectra. It is shown that the selected component of M&ouml, ssbauer reflectivity with rotated polarization is characterized by enhanced surface sensitivity, determined by the &ldquo, squared standing waves&rdquo, depth dependence. Therefore, the new approach has interesting perspectives for investigations of surfaces, ultrathin layers and multilayers having complicated magnetic structures.

Physical review letters 123(9), 097402 (2019). doi:10.1103/PhysRevLett.123.097402, Hard-x-ray spectroscopy relies on a suite of modern techniques for studies of vibrational, electronic, andmagnetic excitations in condensed matter. At present, the energy resolution of these techniques can beimproved only by decreasing the spectral window of the involved optics—monochromators and analyzers—thereby sacrificing the intensity. Here,we demonstrate hard-x-ray spectroscopy with greatly improved energyresolution without narrowing the spectral window by adapting principles of spectrographic imaging tothe hard-x-ray regime. Similar to Newton’s classical prism, the hard-x-ray spectrograph disperses different“colors”—i.e., energies—of x-ray photons in space. Then, selecting each energy component with a slit ensureshigh energy resolution, whereas measuring x-ray spectra with all components of a broad spectral windowkeeps the intensity. We employ the principles of spectrographic imaging for phonon spectroscopy. Here thenew approach revealed anomalous soft atomic dynamics in α-iron, a phenomenon which was not previouslyreported in the literature.We argue that hard-x-ray spectrographic imaging also could be a path to discoveringnew physics in studies of electronic and magnetic excitations., Published by APS, College Park, Md.

Kossel line patterns contain information on the crystalline structure, such as the magnitude and the phase of Bragg reflections. For technical reasons, most of these patterns are obtained using electron beam excitation, which leads to surface sensitivity that limits the spatial extent of the structural information. To obtain the atomic structure in bulk volumes, X-rays should be used as the excitation radiation. However, there are technical problems, such as the need for high resolution, low noise, large dynamic range, photon counting, two-dimensional pixel detectors and the small spot size of the exciting beam, which have prevented the widespread use of Kossel pattern analysis. Here, an experimental setup is described, which can be used for the measurement of Kossel patterns in a reasonable time and with high resolution to recover structural information.

We report on the elastic properties of Ni/[Fe(CN)6] Prussian‐blue‐analogue nanoparticles investigated by high‐pressure synchrotron X‐ray diffraction and nuclear inelastic scattering. For 3 nm and 115 nm particles, we have obtained bulk moduli of (30.3 ± 3.8) GPa and (24.5 ± 3.2) GPa, with Debye sound velocities of (2496 ± 46) m s–1 and (2407 ± 38) m s–1, respectively. Combining these results, Poisson's ratio, Young's modulus, the shear modulus, and the transversal/longitudinal sound velocities have been calculated for each particle size. All of these physical quantities suggest a stiffening of the lattice when the particle size decreases, which is mainly attributed to the reduction of iron ions on the particle surface.\ud \ud The elastic behavior of Prussian‐blue‐analogue nanoparticles has been investigated, using high‐pressure synchrotron X‐ray diffraction and nuclear‐inelastic‐scattering techniques. We have extracted all of the elastic moduli for different sizes of Prussian‐blue‐analogue nanoparticles. This result is the basis for understanding electron–lattice coupling phase transitions at the nanoscale.

Nature Communications 9(1), 4142 (2018). doi:10.1038/s41467-018-06457-x, A Verwey-type charge-ordering transition in magnetite at 120 K leads to the formation of linear units of three iron ions with one shared electron, called trimerons. The recently-discovered iron pentoxide (Fe$_4$O$_5$) comprising mixed-valent iron cations at octahedral chains, demonstrates another unusual charge-ordering transition at 150 K involving competing formation of iron trimerons and dimerons. Here, we experimentally show that applied pressure can tune the charge-ordering pattern in Fe$_4$O$_5$ and strongly affect the ordering temperature. We report two charge-ordered phases, the first of which may comprise both dimeron and trimeron units, whereas, the second exhibits an overall dimerization involving both the octahedral and trigonal-prismatic chains of iron in the crystal structure. We link the dramatic change in the charge-ordering pattern in the second phase to redistribution of electrons between the octahedral and prismatic iron chains, and propose that the average oxidation state of the iron cations can pre-determine a charge-ordering pattern., Published by Nature Publishing Group UK, [London]

Acireductone dioxygenase (ARD) is an intriguing enzyme from the methionine salvage pathway that is capable of catalysing two different oxidation reactions with the same substrate depending on the type of the metal ion in the active site. To date, the structural information regarding the ARD–acireductone complex is limited and possible reaction mechanisms are still under debate. The results of joint experimental and computational studies undertaken to advance knowledge about ARD are reported. The crystal structure of an ARD from Homo sapiens was determined with selenomethionine. EPR spectroscopy suggested that binding acireductone triggers one protein residue to dissociate from Fe(2+), which allows NO (and presumably O(2)) to bind directly to the metal. Mössbauer spectroscopic data (interpreted with the aid of DFT calculations) was consistent with bidentate binding of acireductone to Fe(2+) and concomitant dissociation of His88 from the metal. Major features of Fe vibrational spectra obtained for the native enzyme and upon addition of acireductone were reproduced by QM/MM calculations for the proposed models. A computational (QM/MM) study of the reaction mechanisms suggests that Fe(2+) promotes O—O bond homolysis, which elicits cleavage of the C1—C2 bond of the substrate. Higher M(3+) /M(2+) redox potentials of other divalent metals do not support this pathway, and instead the reaction proceeds similarly to the key reaction step in the quercetin 2,3-dioxygenase mechanism.

Nature geoscience 11(2), 144 - 147 (2018). doi:10.1038/s41561-017-0055-7, The oxidation state of iron in Earth’s mantle is well known to depths of approximately 200 km, but has not been characterized in samples from the lowermost upper mantle (200–410 km depth) or the transition zone (410–660 km depth). Natural samples from the deep (>200 km) mantle are extremely rare, and are usually only found as inclusions in diamonds. Here we use synchrotron Mössbauer source spectroscopy complemented by single-crystal X-ray diffraction to measure the oxidation state of Fe in inclusions of ultra-high pressure majoritic garnet in diamond. The garnets show a pronounced increase in oxidation state with depth, with Fe$^{3+}$/(Fe$^{3+}$+ Fe$^{2+}$) increasing from 0.08 at approximately 240 km depth to 0.30 at approximately 500 km depth. The latter majorites, which come from pyroxenitic bulk compositions, are twice as rich in Fe$^{3+}$ as the most oxidized garnets from the shallow mantle. Corresponding oxygen fugacities are above the upper stability limit of Fe metal. This implies that the increase in oxidation state is unconnected to disproportionation of Fe$^{2+}$ to Fe$^{3+}$ plus Fe$^0$. Instead, the Fe$^{3+}$ increase with depth is consistent with the hypothesis that carbonated fluids or melts are the oxidizing agents responsible for the high Fe$^{3+}$ contents of the inclusions., Published by Nature Publ. Group, London

The use of single molecule magnets (SMMs) as cornerstone elements in spintronics and quantum computing applications demands that magnetic bistability is retained when molecules are interfaced with solid conducting surfaces. Here, we employ synchrotron Mössbauer spectroscopy to investigate a monolayer of a tetrairon(III) (Fe4) SMM chemically grafted on a gold substrate. At low temperature and zero magnetic field, we observe the magnetic pattern of the Fe4 molecule, indicating slow spin fluctuations compared to the Mössbauer timescale. Significant structural deformations of the magnetic core, induced by the interaction with the substrate, as predicted by ab initio molecular dynamics, are also observed. However, the effects of the modifications occurring at the individual iron sites partially compensate each other, so that slow magnetic relaxation is retained on the surface. Interestingly, these deformations escaped detection by conventional synchrotron-based techniques, like X-ray magnetic circular dichroism, thus highlighting the power of synchrotron Mössbauer spectroscopy for the investigation of hybrid interfaces., Deposition of single molecule magnets onto surfaces is a key step for integration in devices exploiting their magnetic bistability and quantum properties. Here, Sessoli and colleagues exploit synchrotron Mössbauer spectroscopy to assess the effects of molecule-surface interactions on the magnetic properties of Fe(III) SMMs.

Before the Archean to Proterozoic Transition (APT) the tectonic regime was dominated by microplates floating on a low viscosity mantle. Such a regime restricted chemical exchange between the shallow and deeper mantle reservoirs. After the APT, a more global convection regime led to deep subduction of slabs. We propose that the improved vertical mixing of the mantle favoured the release to the Earth's surface of an oxygen excess initially trapped in the deep mantle. This excess built up when the primordial lower mantle was left with a high Fe3+/(Fe2++Fe3+) ratio (#Fe3+), after metallic iron segregated down into the core. Our synchrotron-based in situ experiments suggest a primordial Fe3+excess of ∼20 % for the mantle iron. By comparison with the #Fe3+ of the present mantle, this Fe3+excess would correspond to 500-1000 times the O2 content in the Earth's atmosphere. The tectonic transition greatly facilitated the ascent of oxidised lower mantle material towards the Earth's surface, inducing a continuous arrival of O2 at the Earth's surface and into the atmosphere.

Das Protein LytB/ISPH katalysiert den letzten Schritt des Methylerythritolphosphat(MEP)-Wegs, der zur Terpenoidbiosynthese in vielen pathogenen Bakterien dient. Deswegen gilt der MEP-Weg als Angriffspunkt fur neue potentielle Antibiotika, da er essenziell fur Mikroorganismen ist, beim Menschen jedoch nicht vorkommt. Substratfreies LytB hat einen besonderen [4Fe-4S]2+-Cluster mit einer bisher unbekannten Struktur. Experimente mit nuklearer inelastischer Streuung (NIS, oder “nuclear resonance vibrational spectroscopy”, NRVS) in Kombination mit quantenchemischen-molekulmechanischen (QM/MM) Rechnungen zeigen, dass das apikale Eisen des Clusters eindeutig mit drei Wassermolekulen koordiniert ist. Zusatzlich prasentieren wir NIS-Experimente von LytB gebunden mit dem naturlichen Substrat (E)-4-Hydroxy-3-methylbut-2-en-1-yl-diphosphat (HMBPP) sowie mit den Inhibitoren (E)-4-Amino-3-methylbut-2-en-1-yl-diphosphat und (E)-4-Mercapto-3-methylbut-2-en-1-yl-diphosphat.

The LytB/IspH protein catalyzes the last step of the methylerythritol phosphate (MEP) pathway which is used for the biosynthesis of essential terpenoids in most pathogenic bacteria. Therefore, the MEP pathway is a target for the development of new antimicrobial agents as it is essential for microorganisms, yet absent in humans. Substrate-free LytB has a special [4Fe-4S](2+) cluster with a yet unsolved structure. This motivated us to use synchrotron-based nuclear resonance vibrational spectroscopy (NRVS) in combination with quantum chemical-molecular mechanical (QM/MM) calculations to gain more insight into the structure of substrate-free LytB. The apical iron atom of the [4Fe-4S](2+) is clearly linked to three water molecules. We additionally present NRVS data of LytB bound to its natural substrate, (E)-4-hydroxy-3-methylbut-2-en-1-yl diphosphate (HMBPP) and to the inhibitors (E)-4-amino-3-methylbut-2-en-1-yl diphosphate and (E)-4-mercapto-3-methylbut-2-en-1-yl diphosphate.

Mössbauer reflectivity spectra and nuclear resonance reflectivity (NRR) curves have been measured using the Synchrotron Mössbauer Source (SMS) for a [

International audience; Metallic phases in the Tazewell IIICD iron and Esquel pallasite meteorites were examined using Fe-57 synchrotron Mossbauer spectroscopy. Spatial resolution of 10-20m was achieved, together with high throughput, enabling individual spectra to be recorded in less than 1h. Spectra were recorded every 5-10m, allowing phase fractions and hyperfine parameters to be traced along transects of key microstructural features. The main focus of the study was the transitional region between kamacite and plessite, known as the cloudy zone. Results confirm the presence of tetrataenite and antitaenite in the cloudy zone as its only components. However, both phases were also found in plessite, indicating that antitaenite is not restricted exclusively to the cloudy zone, as previously thought. The confirmation of paramagnetic antitaenite as the matrix phase of the cloudy zone contrasts with recent observations of a ferromagnetic matrix phase using X-ray photoemission electron spectroscopy. Possible explanations for the different results seen using these techniques are proposed

We describe a new methodology to collect energy domain Mossbauer spectra of inclusions in natural diamonds using a Synchrotron Mossbauer Source (SMS). Measurements were carried out at the Nuclear Resonance beamline ID18 at the European Synchrotron Radiation Facility (Grenoble, France). We applied this non-destructive approach to collect SMS spectra of a ferropericlase inclusion still contained within its diamond host from Juina (Brazil). The high spatial resolution of the measurement (~ 15 μm) enabled multiple regions of the 190 × 105 μm 2 inclusion to be sampled and showed that while Fe 3 + /Fe tot values in ferropericlase were below the detection limit (0.02) overall, there was a magnetic component whose abundance varied systematically across the inclusion. Hyperfine parameters of the magnetic component are consistent with magnesioferrite, and the absence of superparamagnetism allows the minimum particle size to be estimated as ~ 30 nm. Bulk Fe 3 + /Fe tot values are similar to those reported for other ferropericlase inclusions from Juina, and their variation across the inclusion can provide constraints on its history.

Elastic wave velocities of minerals are important for constraining the chemistry, structure and dynamics of the Earth’s mantle based on the comparison between laboratory-based measurements and seismic observations. As the second most abundant phase in the Earth’s lower mantle, (Mg,Fe)O ferropericlase has been the focus of numerous studies measuring the elastic wave velocities using various methods such as Brillouin spectroscopy and ultrasonic measurements. Recently, nuclear inelastic scattering (NIS) has been used to determine elastic wave velocities of iron-bearing phases. However, the elastic wave velocities of ferropericlase obtained using NIS are considerably lower than the velocities obtained by other methods, even at ambient conditions. One possible source of this discrepancy is the local nature of the NIS method. In order to test this hypothesis, we have investigated six ferropericlase samples with various iron contents using NIS. The Debye sound velocities calculated using the conventional method of NIS analysis are consistent with previous results obtained using NIS, yet the values are significantly lower than those obtained using ultrasonics and Brillouin spectroscopy. If the Debye sound velocities are re-calculated based on a mixture of different iron next-neighbour configurations with different compositions, the Debye sound velocities determined by NIS agree well with the results from other methods. Our new model was also successfully applied to high-pressure NIS data taken from the literature. Our results constitute an important step towards a better understanding of how to obtain reliable sound velocities of iron-bearing mantle minerals from NIS measurements.

Biogeochemistry investigates chemical cycles which influence or are influenced by biological activity. Astrobiology studies the origin, evolution and distribution of life in the universe. The biogeochemical Fe cycle has controlled major nutrient cycles such as the C cycle throughout geological time. Iron sulfide minerals may have provided energy and surfaces for the first pioneer organisms on Earth. Banded iron formations document the evolution of oxygenic photosynthesis. To assess the potential habitability of planets other than Earth one looks for water, an energy source and a C source. On Mars, for example, Fe minerals have provided evidence for the past presence of liquid water on its surface and would provide a viable energy source. Here we present Mössbauer spectroscopy investigations of Fe and C cycle interactions in both ancient and modern environments. Experiments to simulate the diagenesis of banded iron formations indicate that the formation of ferrous minerals depends on the amount of biomass buried with ferric precursors rather than on the atmospheric composition at the time of deposition. Mössbauer spectra further reveal the mutual stabilisation of Fe-organic matter complexes against mineral transformation and decay of organic matter into CO2. This corresponds to observations of a ‘rusty carbon sink’ in modern sediments. The stabilisation of Fe-organic matter complexes may also aid transport of particulate Fe in the water column while having an adverse effect on the bioavailability of Fe. In the modern oxic ocean, Fe is insoluble and particulate Fe represents an important source. Collecting that particulate Fe yields small sample sizes that would pose a challenge for conventional Mössbauer experiments. We demonstrate that the unique properties of the beam used in synchrotron-based Mössbauer applications can be utilized for studying such samples effectively. Reactive Fe species often occur in amorphous or nanoparticulate form in the environment and are therefore difficult to study with standard mineralogical tools. Sequential extraction techniques are commonly used as proxies. We provide an example where Mössbauer spectroscopy can replace sequential extraction techniques where mineralogical information is sought. Where mineral separation is needed, for example in the investigation of Fe or S isotope fractionation, Mössbauer spectroscopy can help to optimize sequential extraction procedures. This can be employed in a large number of investigations of soils and sediments, potentially even for mineral separation to study Fe and S isotope fractionation in samples returned from Mars, which might reveal signatures of biological activity. When looking for the possibility of life outside Earth, Jupiter’s icy moon Europa is one of the most exciting places. It may be just in reach for a Mössbauer spectrometer deployed by a future lander to study the red streak mineral deposits on its surface to look for clues about the composition of the ocean hidden under the moon’s icy surface. Universities of Bayreuth and Tubingen funded through the DFG research unit FOR 580 electron transfer processes in anoxic aquifers (e-TraP); an Impact Fellowship awarded by the University of Stirling; and a SAGES PECRE grant. Parts of this work were supported by research grants (KA 1736/4-1 and 12-1) from the German Research Foundation (DFG). Scopus

The physical properties of disordered systems are in the focus of a large research effort. In particular, one of the open problems related to glasses is their excess of modes in the THz frequency range over the vibrational contribution predicted by the Debye model. In fact, one could expect the continuum approximation underlying the Debye model to hold in glasses at long wavelengths at least as well as in crystalline solids. Experiments, instead, seem to indicate that the specific heat at low temperature (a few Kelvin) and the density of vibrational states at low frequency (a few terahertz) are very different from the Debye prediction. We present here a detailed analysis of specific heat measurements of vitreous GeO2, a prototype of strong glasses, and of permanently densified vitreous GeO2. Our data give experimental evidence that glasses do not show any excess of vibrational modes when compared to their crystalline counterparts of similar mass density.

Progress in Earth and Planetary Science 3(1), 10 (2016). doi:10.1186/s40645-016-0089-2, Sound velocities of bridgmanite measured in the laboratory are a key to deciphering the composition of the lower mantle. Here, we report Debye sound velocities determined using nuclear inelastic scattering (NIS) for one majorite composition (Mg0.82Fe0.18SiO3) and five bridgmanite compositions (Mg$_{0.82}$Fe$_{0.18}$SiO$_3$, Mg$_{0.86}$Fe$_{0.14}$Si$_{0.98}$Al$_{0.02}$O$_3$, Mg$_{0.88}$Fe$_{0.12}$SiO$_3$, Mg$_{0.6}$Fe$_{0.4}$Si$_{0.63}$Al$_{0.37}$O$_3$, Mg$_{0.83}$Fe$_{0.15}$Si$_{0.98}$Al$_{0.04}$O$_3$) measured in a diamond anvil cell at pressures up to 89 GPa at room temperature. Debye sound velocities for majorite determined from NIS are consistent with literature data from Brillouin scattering and ultrasonics, while Debye sound velocities for bridgmanite are significantly lower than literature values from the same methods. We calculated partial and total density of states (DOS) for MgSiO$_3$ and FeSiO$_3$ bridgmanite using density functional theory and demonstrate that Debye sound velocities calculated from the reduced DOS using the same approach as for the experimental data (i.e., the limit of D(E)/E$^2$ as energy goes to zero) give the same sound velocities for each phase irrespective of which partial DOS is used. In addition, we show that Debye sound velocities calculated using this approach are consistent with values obtained from the calculation of the full elastic tensor. Comparison of the calculated DOS with the one obtained from NIS indicates that the experimental DOS has enhanced intensity at low energies that leads to a different slope of the DOS and hence a lower sound velocity. This effect is present in all of the bridgmanite samples examined in this study., Published by Springer Open, Berlin

International audience; We report on a combined nuclear inelastic scattering and metal isotope substitution based Raman spectroscopic investigation of lattice dynamics changes associated with the spin transition in the ferrous complex [Fe(H2B(pz)(2))(2)(phen)] (pz = pyrazolyl, phen = 1,10-phenantroline). These techniques allowed us to identify Raman active metal - ligand stretching vibrations in the high spin (v(HS) = 232 cm(-1)) and low spin (v(LS) = 390 cm(-1)) states as well as to calculate associated changes of the Debye temperature (Theta(HS)(D) = 140 K, Theta(LS)(D) = 146 K), Debye sound velocity (v(HS) = 1282 m/s, v(LS) = 1300 m/s) and Young's modulus (E-HS = 4.7 GPa, E-LS = 5.2 GPa).