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In this work, we use extended X-ray absorption fine structure (EXAFS) data collected using nano-polycrystalline diamond anvil cell to study the atomic arrangement in Zr–Cu metallic glass in high pressure (HP) conditions. To reveal the microscopic details of stress accommodation mechanism, we performed molecular dynamics (MD) simulations of the HP atomic arrangement. By comparing the experimental and the calculated Zr and Cu K-edge EXAFS signal we prove the realistic character of the computer simulations. A detailed geometrical analysis of the simulated atomic configurations shows that with increasing hydrostatic pressure the local structure of Zr–Cu amorphous alloy becomes gradually dominated by Cu-centred icosahedral structural motifs involving fivefold symmetry incompatible with crystalline ordering. The variation of the short-range order is attributed to preferential straining of mechanically soft bonds between zirconium atoms. [ABSTRACT FROM AUTHOR]

We present a combined high pressure Ni K-edge x-ray absorption and Raman spectroscopic investigation of β-Ni(OH). Extended x-ray absorption fine structure analysis reveals a progressive shrinking of the Ni–O and Ni–Ni bond distances with pressure. As pressure is increased, Raman data show a continuous hardening of the phonon modes associated with the vibration of Ni–O sublattice, whereas a systematic frequency softening is displayed by the hydroxyl (O–H) symmetric stretching mode. This contrasting behavior implies a gradual development of a lattice instability with pressure in nickel hydroxide. Under pressure hydrogen bonds become increasingly unstable mainly due to the displacement of H atoms around the Ni–O axis inducing a local-lattice instability may explain the structural, Raman and x-ray absorption results. [ABSTRACT FROM AUTHOR]

We present in this paper recent advances in the high pressure domain provided by the introduction of time-resolved energy-dispersive XAS (EDXAS) techniques at synchrotrons. We highlight technical aspects and describe two modes of acquisition: the ‘movie’ mode, where the time resolution is given by the detector acquisition speed and the ‘pump-and-probe’ mode, where the time resolution is given by the delay between the pump and the probe. These two modes define a frontier in the time resolution, respectively above and below the ∼10 μs regime. In the former, examples of applications are chemical stability and reactions at high pressure and high temperature or probing the warm dense matter regime using rapid current ramps. In the latter, an example is given on studies of dynamically compressed matter, by coupling single-bunch EDXAS at high-brilliance synchrotron to a nanosecond high-power laser. [ABSTRACT FROM PUBLISHER]

Double-sided laser heating (LH) combined with synchrotron X-ray radiation forin situstudies in the diamond anvil cell (DAC) has been the most productive and widely used high-temperature–high pressure technique in the past two decades. In the framework of the UPBL11 project (upgrade of ID24 beamline of European Synchrotron Radiation Facility), we developed a new on-line LH system for DACs. The preliminary optical scheme of the system is presented and discussed. Varying the settings, we are able to shape and to size the beam on the surface of the sample in the DAC. First pilot applications to the Fe case are shown. [ABSTRACT FROM AUTHOR]

Despite a large number of studies of iron spin state in silicate perovskite at high pressure and high temperature, there is still disagreement regarding the type and P– T conditions of the transition, and whether Fe2+ or Fe3+ or both iron cations are involved. Recently, our group published results of a Mössbauer spectroscopy study of the iron behaviour in (Mg,Fe)(Si,Al)O3 perovskite at pressures up to 110 GPa (McCammon et al. ), where we suggested stabilization of the intermediate spin state for 8- to 12-fold coordinated ferrous iron ([8–12]Fe2+) in silicate perovskite above 30 GPa. In order to explore the behaviour in related systems, we performed a comparative Mössbauer spectroscopic study of silicate perovskite (Fe0.12Mg0.88SiO3) and majorite (with two compositions—Fe0.18Mg0.82SiO3 and Fe0.11Mg0.88SiO3) at pressures up to 81 GPa in the temperature range 296–800 K, which was mainly motivated by the fact that the oxygen environment of ferrous iron in majorite is quite similar to that in silicate perovskite. The [8–12]Fe2+ component, dominating the Mössbauer spectra of majorites, shows high quadrupole splitting (QS) values, about 3.6 mm s−1, in the entire studied P– T region (pressures to 58 GPa and 296–800 K). Decrease of the QS of this component with temperature at constant pressure can be described by the Huggins model with the energy splitting between low-energy e g levels of [8–12]Fe2+ equal to 1,500 (50) cm−1 for Fe0.18Mg0.82SiO3 and to 1,680 (70) cm−1 for Fe0.11Mg0.88SiO3. In contrast, for the silicate perovskite dominating Mössbauer component associated with [8–12]Fe2+ suggests the gradual change of the electronic properties. Namely, an additional spectral component with central shift close to that for high-spin [8–12]Fe2+ and QS about 3.7 mm s−1 appeared at ~35 (2) GPa, and the amount of the component increases with both pressure and temperature. The temperature dependence of QS of the component cannot be described in the framework of the Huggins model. Observed differences in the high-pressure high-temperature behaviour of [8–12]Fe2+ in the silicate perovskite and majorite phases provide additional arguments in favour of the gradual high-spin—intermediate-spin crossover in lower mantle perovskite, previously reported by McCammon et al. () and Lin et al. (). [ABSTRACT FROM AUTHOR]

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 Ce 55 Al 45 and Ce 75 Al 25 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 Ce 55 Al 45 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 Ce 75 Al 25 alloy which eventually leads to its devitrification at 25 GPa. [ABSTRACT FROM AUTHOR]