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International audience; Seismic anisotropy in Earth's lowermost mantle, resulting from Crystallographic Preferred Orientation (CPO) of elastically anisotropic minerals, is among the most promising observables to map mantle flow patterns. A quantitative interpretation, however, is hampered by the limited understanding of CPO development in lower mantle minerals at simultaneously high pressures and temperatures. Here, we experimentally determine CPO formation in ferropericlase, one of the elastically most anisotropic deep mantle phases, at pressures of the lower mantle and temperatures of up to 1400 K using a novel experimental setup. Our data reveal a significant contribution of slip on (100) to ferropericlase CPO in the deep lower mantle, contradicting previous inferences based on experimental work at lower mantle pressures but room temperature. We use our results along with a geodynamic model to show that deformed ferropericlase produces strong shear wave anisotropy in the lowermost mantle, where horizontally polarized shear waves are faster than vertically polarized shear waves, consistent with seismic observations. We find that ferropericlase alone can produce the observed seismic shear wave splitting in D" in regions of downwelling, which may be further enhanced by post-perovskite. Our model further shows that the interplay between ferropericlase (causing VSH > Vsv) and bridgmanite (causing Vsv > VSH) CPO can produce a more complex anisotropy patterns as observed in regions of upwelling at the margin of the African Large Low Shear Velocity Province.

Geophysical research letters 45(14), 6862 - 6868 (2018). doi:10.1029/2018GL077982, We experimentally determined the bulk modulus of (Mg$_{0.8}$Fe$_{0.2}$)O ferropericlase across theiron spin transition and in the low-spin phase by employing a new experimental approach. In ourmeasurements, we simulate the propagation of a compressional seismic wave (P wave) through our sampleby employing a piezo-driven dynamic diamond anvil cell that allows to oscillate pressure at seismicfrequencies. During pressure oscillations, X-ray diffraction images were continuously collected every5–50 ms. The bulk modulus is directly calculated from these data at different pressures. Our experimentsshow a pronounced softening of the bulk modulus throughout the spin crossover, supporting previoussingle-crystal measurements at very high frequencies and computations. Comparison of our results toprevious data collected on (Mg,Fe)O with lower iron contents shows that the magnitude of softening stronglydepends on iron content. Our experiments at seismic frequencies confirm that the iron spin crossovermarkedly affects the ratio of seismic compressional to shear wave velocities in Earth’s lower mantle., Published by Wiley, Hoboken, NJ

Scientific reports 7(1), 1139 (2017). doi:10.1038/s41598-017-01233-1, Synchrotron x-ray diffraction reveals a pressure induced crystallization at about 3.4 GPa and a polymorphic transition near 10.3 GPa when compressed a liquid GaIn eutectic alloy up to ~13 GPa at room temperature in a diamond anvil cell. Upon decompression, the high pressure crystalline phase remains almost unchanged until it transforms to the liquid state at around 2.3 GPa. The ab initio molecular dynamics calculations can reproduce the low pressure crystallization and give some hints on the understanding of the transition between the liquid and the crystalline phase on the atomic level. The calculated pair correlation function g(r) shows a non-uniform contraction reflected by the different compressibility between the short (1st shell) and the intermediate (2nd to 4th shells). It is concluded that the pressure-induced liquid-crystalline phase transformation likely arises from the changes in local atomic packing of the nearest neighbors as well as electronic structures at the transition pressure., Published by Nature Publishing Group, London

Seismic anisotropy in Earth’s lowermost mantle, resulting from crystallographic preferred orientation (CPO) of elastically anisotropic minerals, is the most promising observable to map mantle flow patterns. The shear wave anisotropy observed in the lowermost mantle might be caused by CPO of (Mg,Fe)O ferropericlase that is characterized by large elastic anisotropy in the deep lower mantle. However, our understanding of the slip system activities of ferropericlase at conditions of the lowermost mantle is still incomplete. Here, we present results of an experimental study designed to determine slip system activities in (Mg,Fe)O at P-T conditions of the lower mantle. In-situ deformation experiments on powders of (Mg0.8Fe0.2)O were conducted in a graphite heated diamond anvil cell (DAC) up to a temperature of 1400K. Synchrotron x-ray diffraction data were fit with the program MAUD (Materials Analysing Using Diffraction) to extract textures and lattice strains. The experimental results were modelled using the Elasto-Viscoplastic Self Consistent (EVPSC) code. Our data indicate a change in slip system activities from dominant {110} to increasing {100} slip at temperatures above 1150 K and pressures corresponding to the mid-lower mantle. Our findings indicate an effect of both pressure and temperature on the plasticity of (Mg,Fe)O and, hence, pave the way to a better understanding of with a potential change of dominant slip system between 40-60 GPa in MgO predicted from numerical models (Amodeo et al., 2012). We use the results to model the possible contribution of ferropericlase CPO to observed seismic anisotropy in the D’’ layer in the lowermost mantle.

Journal of applied physics 121(23), 235901 (2017). doi:10.1063/1.4984796, The stability of high-entropy alloys (HEAs) is a key issue before their selection for industrial applications. In this study, in-situ high-pressure and high-temperature synchrotron radiation X-ray diffraction experiments have been performed on three typical HEAs Ni$_{20}$Co$_{20}$Fe$_{20}$Mn$_{20}$Cr$_{20}$, Hf$_{25}$Nb$_{25}$Zr$_{25}$Ti$_{25}$, and Re$_{25}$Ru$_{25}$Co$_{25}$Fe$_{25}$ (at. %), having face-centered cubic (fcc), body-centered cubic (bcc), and hexagonal close-packed (hcp) crystal structures, respectively, up to the pressure of ∼80 GPa and temperature of ∼1262 K. Under the extreme conditions of the pressure and temperature, all three studied HEAs remain stable up to the maximum pressure and temperatures achieved. For these three types of studied HEAs, the pressure-dependence of the volume can be well described with the third order Birch-Murnaghan equation of state. The bulk modulus and its pressure derivative are found to be 88.3 GPa and 4 for bcc-Hf$_{25}$Nb$_{25}$Zr$_{25}$Ti$_{25}$, 193.9 GPa and 5.9 for fcc-Ni$_{20}$Co$_{20}$Fe$_{20}$Mn$_{20}$Cr$_{20}$, and 304.6 GPa and 3.8 for hcp-Re$_{25}$Ru$_{25}$Co$_{25}$Fe$_{25}$ HEAs, respectively. The thermal expansion coefficient for the three studied HEAs is found to be in the order as follows: fcc-Ni$_{20}$Co$_{20}$Fe$_{20}$Mn$_{20}$Cr$_{20}$ > bcc-Hf$_{25}$Nb$_{25}$Zr$_{25}$Ti$_{25}$ ≈ hcp-Re$_{25}$Ru$_{25}$Co$_{25}$Fe$_{25}$., Published by American Inst. of Physics, Melville, NY

第7回極域科学シンポジウム:[OA] 南極隕石/はやぶさ11月30日（水）国立国語研究所 2階講堂

Physical review / B 94(19), 195211 (2016). doi:10.1103/PhysRevB.94.195211, In pressure-induced reversible structural transitions, the term “reversible” refers to the recovery of the virgin structure in a material upon complete decompression. Pressure-induced amorphous-to-crystalline transitions have been claimed to be reversible, but evidence that amorphous material recovers its virgin amorphous structure upon complete depressurization has been lacking. In amorphous $As_{2}Se_{3} (a−As_{2}Se_{3})$ chalcogenide, however, we report a novel reversible amorphous-to-crystalline transition that provides compelling experimental evidence that upon complete decompression, the recovered amorphous phase is structurally the same as that of the virgin (as-cast) amorphous phase. Combining the experimental results with ab initio molecular dynamics simulations, we elucidate that the amorphization is mediated by a surplus of total free energy in the high-pressure face-centered cubic phase as compared to the virgin amorphous phase and that the structural recovery to the virgin amorphous phase is a consequence of an enhancement in covalent bonding character over interlayer forces upon complete decompression. Furthermore, we observed a two-dimensional to three-dimensional network transition under compression and its reversibility upon decompression., Published by APS, Woodbury, NY

In pressure-induced reversible structural transitions, the term “reversible” refers to the recovery of the virginstructure in a material upon complete decompression. Pressure-induced amorphous-to-crystalline transitionshave been claimed to be reversible, but evidence that amorphous material recovers its virgin amorphous structureupon complete depressurization has been lacking. In amorphous As$_2$Se$_3$ (a-As$_2$Se$_3$) chalcogenide, however, wereport a novel reversible amorphous-to-crystalline transition that provides compelling experimental evidencethat upon complete decompression, the recovered amorphous phase is structurally the same as that of the virgin(as-cast) amorphous phase. Combining the experimental results with ab initio molecular dynamics simulations,we elucidate that the amorphization ismediated by a surplus of total free energy in the high-pressure face-centeredcubic phase as compared to the virgin amorphous phase and that the structural recovery to the virgin amorphousphase is a consequence of an enhancement in covalent bonding character over interlayer forces upon completedecompression. Furthermore, we observed a two-dimensional to three-dimensional network transition undercompression and its reversibility upon decompression.

In pressure-induced reversible structural transitions, the term "reversible" refers to the recovery of the virgin structure in a material upon complete decompression. Pressure-induced amorphous-to-crystalline transitions have been claimed to be reversible, but evidence that amorphous material recovers its virgin amorphous structure upon complete depressurization has been lacking. In amorphous As2Se3 (a-As2Se3) chalcogenide, however, we report a novel reversible amorphous-to-crystalline transition that provides compelling experimental evidence that upon complete decompression, the recovered amorphous phase is structurally the same as that of the virgin (as-cast) amorphous phase. Combining the experimental results with ab initio molecular dynamics simulations, we elucidate that the amorphization is mediated by a surplus of total free energy in the high-pressure face-centered cubic phase as compared to the virgin amorphous phase and that the structural recovery to the virgin amorphous phase is a consequence of an enhancement in covalent bonding character over interlayer forces upon complete decompression. Furthermore, we observed a two-dimensional to three-dimensional network transition under compression and its reversibility upon decompression.

A detailed description is presented of the Extreme Conditions Beamline P02.2 for micro X-ray diffraction studies of matter at simultaneous high pressure and high/low temperatures at PETRA III, in Hamburg, Germany. This includes performance of the X-ray optics and instrumental resolution as well as an overview of the different sample environments available for high-pressure studies in the diamond anvil cell. Particularly emphasized are the high-brilliance and high-energy X-ray diffraction capabilities of the beamline in conjunction with the use of fast area detectors to conduct time-resolved compression studies in the millisecond time regime. Finally, the current capability of the Extreme Conditions Science Infrastructure to support high-pressure research at the Extreme Conditions Beamline and other PETRA III beamlines is described.

The magnetic, structural, and vibrational properties of YMn${_2}$O${_5}$ multiferroic have been studied bymeans of neutron, x-ray powder diffraction, and Raman spectroscopy at pressures up to 6 and 30 GPa,respectively. Application of high pressure,P >1 GPa, leads to a gradual suppression of the commensurate andincommensurate antiferromagnetic (AFM) phaseswith a propagation vector q = (1/2,0,q${_z}$∼1/4) and appearanceof the commensurate AFM phase with q = (1/2,0,1/2). This observation is sharply contrasting to general trendtowards stabilization of commensurate AFM phase with q = (1/2,0,1/4) found in other RMn${_2}$O${_5}$ compoundsupon lattice compression. At P ∼ 16 GPa a structural phase transformation accompanied by anomalies in latticecompression and pressure behavior of vibrational modeswas observed. The comparative analysis of high-pressureand R-cation radius variation effects clarified a role of particular magnetic interactions in the formation of themagnetic states of RMn${_2}$O${_5}$ compounds.

Acta materialia 81, 420 - 427 (2014). doi:10.1016/j.actamat.2014.08.051, In situ high-pressure X-ray diffraction experiments and reverse Monte Carlo simulations on Pd81Si19 glassy alloy were performed up to ∼35 GPa. High-quality structure factor data with a q range up to 13.5 Å$^{−1}$ were obtained. The pressure dependence of the relative volume of Pd$_{81}$Si$_{19}$ glassy alloy can be well described by a third-order Birch–Murnaghan equation of state with bulk modulus of $B^0 $ = 229 GPa and a pressure derivative of $B'_{0}$. The continuous and monotonic change of relative volume as a function of pressure does not indicate any first-order phase transitions in Pd$_{81}$Si$_{19}$ glassy alloy in the studied pressure range. The pressure dependence of the atomic structures was systematically investigated by means of bond angle distribution, the Honeycutt and Andersen index, Voronoi tessellation, total and partial coordination numbers, and local chemical ordering analyses. It is found that the topological and chemical atomic structures of the Pd$_{81}$Si$_{19}$ glassy alloy do not change much with pressure, indicating the stability of this material under pressure., Published by Elsevier Science, Amsterdam [u.a.]