-
Sébastien Merkel,
Hans Rudolf Wenk,
Jinfu Shu,
Guoyin Shen,
Philippe Gillet,
Ho-Kwang Mao,
Russell J Hemley,
H R Wenk,
J Shu,
G Shen,
P Gillet,
H K Mao, R J Hemley
[show abstract]
[hide abstract]
ABSTRACT: 1] Room temperature investigations on the shear strength, elastic moduli, elastic anisotropy, and deformation mechanisms of MgO (periclase) are performed in situ up to pressures of 47 GPa using radial X-ray diffraction and the diamond anvil cell. The calculated elastic moduli are in agreement with previous Brillouin spectroscopy studies. The uniaxial stress component in the polycrystalline MgO sample is found to increase rapidly to 8.5(±1) GPa at a pressure of 10(±1) GPa in all experiments. Under axial compression, a strong cube texture develops which was recorded in situ. It is probable that the preferred orientation of MgO is due to deformation by slip. A comparison between the experimental textures and results from polycrystal plasticity suggest that the {110}h1 " 10i is the only significantly active slip system under very high confining pressure at room temperature. These data demonstrate the feasibility of analyzing elastic moduli, shear strength, and deformation mechanisms under pressures relevant for the Earth's lower mantle. Implications for the anisotropy and rheology of the lower mantle are discussed.
J. Geophys. Res. 01/2271; 107.
-
[show abstract]
[hide abstract]
ABSTRACT: The crystal structure of the γ-brass phase Cu5Zn8 is confirmed with single-crystal X-ray diffraction and a charge-coupled device (CCD) detector to be cubic with 52 atoms in
the unit cell, space group
I[`4] 3mI\overline 4 3m
, and the refined atomic positions are in good agreement with previously reported data. The structural behavior of α-(fcc),
β-brass (cI52) phases of the Cu−Zn alloy system has been studied under pressure using diamond anvil cells and powder X-ray diffraction
with synchrotron radiation. The appearance of additional peaks in the diffraction patterns of α- and β-phases indicates the
beginning of transitions to new phases at 17 and 37 GPa, respectively. The complex cubic γ-brass phase (52 atoms in the unit
cell, space group
I[`4] 3mI\overline 4 3m
is observed to be stable up to at least 50 GPa. The bulk modulus K
0 was determined as 140(4) GPa for α-, 139(5) for β-, and 121(2) for γ-phase assuming K
0
′
=4. The structural stability of brass phases of the Cu−Zn system under pressure is discussed in terms of the Hume-Rothery
mechanism.
Metallurgical and Materials Transactions A 05/2012; 37(12):3381-3385. · 1.54 Impact Factor
-
42nd Lunar and Planetary Science Conference. 01/2011; 42:1892.
-
[show abstract]
[hide abstract]
ABSTRACT: Closed electron shell systems, such as hydrogen, nitrogen or group 18 elements, can form weakly bound stoichiometric compounds at high pressures. An understanding of the stability of these van der Waals compounds is lacking, as is information on the nature of their interatomic interactions. We describe the formation of a stable compound in the Xe–H2 binary system, revealed by a suite of X-ray diffraction and optical spectroscopy measurements. At 4.8 GPa, a unique hydrogen-rich structure forms that can be viewed as a tripled solid hydrogen lattice modulated by layers of xenon, consisting of xenon dimers. Varying the applied pressure tunes the Xe–Xe distances in the solid over a broad range from that of an expanded xenon lattice to the distances observed in metallic xenon at megabar pressures. Infrared and Raman spectra indicate a weakening of the intramolecular covalent bond as well as persistence of semiconducting behaviour in the compound to at least 255 GPa.
Nature Chemistry 12/2010; 2. · 20.52 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: There was a discrepancy between the seismic tomography and the elastic property of MgSiO3 perovskite at near the D" zone and core boundary. Since a discovery of post-perovskite (ppv) of MgSiO3, many investigations have made to explain the presence of low seismic velocity of the lower mantle and D" zone. However, precise experimental structure analysis of ppv-(Mg1-xFex)SiO3 has never been reported because of the experimental difficulty. Fe and Mg cation distribution and ordering in ppv-(Mg,Fe)SiO3 in consideration of spins states are significant subject in lower mantle electronic and magnetic states. The present experiment aims X-ray emission study and structure analysis by Rietveld profile fitting of ppv-(Mg0.6,Fe0.4)SiO3 by the precise powder diffraction measurement. Monte Carlo calculation proposed the reliable structures of iron-rich phase of ppv-(Mg,Fe)SiO3: Pmmn, Pmma, and Cm2m and Cmcm proposed by. The best-fit structure model with the highest reliability in the Rietveld fitting of ppv-(Mg0.6Fe0.4)SiO3 is the structure of space group Pmma, in which Fe and Mg occupy two different sites of M1 and M2: the site occupancies are (Fe0.25Mg0.75) in the larger M1 site and (Fe0.55, Mg0.45) in the smaller M2 site. The two-site model is consistence with the previous results of X-ray emission and X-ray Mössbauer experiments.
Journal of Physics Conference Series 04/2010; 215(1):012100.
-
[show abstract]
[hide abstract]
ABSTRACT: The electronic and lattice dynamical properties of compressed solid SiH$_{4}$ have been calculated in the pressure range up to 300 GPa with density functional theory. We find that structures having a layered network with eight-fold SiH$_{8}$ coordination favor metallization and superconductivity. SiH$_{4}$ in these layered structures is predicted to have superconducting transition temperatures ranging from 20 to 80 K, thus presenting new possibilities for exploring high temperature superconductivity in this hydrogen-rich system.
04/2008;
-
[show abstract]
[hide abstract]
ABSTRACT: We report quantitative intensity measurements of the infrared vibron in the high-pressure molecular phase of solid hydrogen above 150 GPa. The results are analyzed in terms of effective static and dynamic charge. The effective charge reaches 0.04e at 230 GPa, which rules out full ionization of the hydrogen molecules to these pressures. The results are consistent with charge transfer associated with orientational ordering in this phase.
EPL (Europhysics Letters) 01/2007; 37(6):403. · 2.17 Impact Factor
-
Y Q Cai,
H-K Mao,
P C Chow,
J S Tse,
Y Ma,
S Patchkovskii,
J F Shu,
V Struzhkin, R J Hemley,
H Ishii,
C C Chen,
I Jarrige,
C T Chen,
S R Shieh,
E P Huang,
C C Kao
[show abstract]
[hide abstract]
ABSTRACT: The near K-edge structure of oxygen in liquid water and ices III, II, and IX at 0.25 GPa and several low temperatures down to 4 K has been studied using inelastic x-ray scattering at 9884.7 eV with a total energy resolution of 305 and 175 meV. A marked decrease of the preedge intensity from the liquid phase and ice III to ices II and IX is attributed to ordering of the hydrogen bonds in the proton-ordered lattice of the latter phases. Density functional theory calculations including the influence of the Madelung potential of the ice IX crystal correctly account for the remaining preedge feature. Furthermore, we obtain spectroscopic evidence suggesting a possible new phase of ice at temperatures between 4 and 50 K.
Physical Review Letters 02/2005; 94(2):025502. · 7.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Room temperature investigations of the single-crystal elastic moduli and anisotropy of the e-phase of iron are performed up to 30.3 GPa using the radial X-ray diffraction technique. The accuracy of the calculated elastic moduli has improved compared to previous measurements using similar techniques because of an increase in accuracy of the measurement, confinement of the sample to limit the effect of plasticity, and better calibration of the stress conditions. The aggregate shear modulus that we obtain is in good agreement with a variety of other experimental deductions but differs from first-principles calculations. The effects of the calibration of stress and micromechanical model on the deduction of elastic moduli and elastic anisotropy are discussed in detail. The anisotropy we obtain has the same order of magnitude as first-principles calculations but the direction is reversed, with a weaker amplitude that previous measurements.
J. Geophys. Res. 01/2005; 110:B05201.
-
[show abstract]
[hide abstract]
ABSTRACT: The crystal structure of the γ -brass phase Cu5Zn8 is confirmed with single-crystal x-ray diffraction and CCD detector to be cubic with 52 atoms in the unit cell, space group I ¯ 43m, and the refined atomic positions are in good agreement with previously reported data. The structural behaviour of α-(fcc), β-(bcc), and γ -brass (cI 52) phases of the Cu–Zn alloy system has been studied under pressure using diamond anvil cells and powder x-ray diffraction with synchrotron radiation. The appearance of additional peaks in the diffraction patterns of α-and β-phases indicates the beginning of transitions to new phases at 17 and 37 GPa, respectively. The complex cubic γ -brass phase is observed to be stable up to at least 50 GPa. The bulk modulus K 0 was determined as 140(4) GPa for α-, 139(5) GPa for β-, and 121(2) GPa for γ -phase assuming K 0 = 4. The structural stability of brass phases of the Cu–Zn system under pressure is discussed in terms of a Hume-Rothery mechanism.
Journal of Physics Condensed Matter 01/2005; 17:7955-7962. · 2.55 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The transformation of molecular nitrogen to a single-bonded atomic nitrogen is of significant interest from a fundamental stand point and because it is the most energetic non-nuclear material predicted. We performed an x-ray diffraction of nitrogen at pressures up to 170 GPa. At 60 GPa, we found a transition from the rhombohedral (R3c) epsilon-N(2) phase to the zeta-N(2) phase, which we identified as orthorhombic with space group P222(1) and with four molecules per unit cell. This transition is accompanied by increasing intramolecular and decreasing intermolecular distances. The major transformation of this diatomic phase into the single-bonded (polymeric) phase, recently determined to have the cubic gauche structure (cg-N), proceeds as a first-order transition with a volume change of 22%.
The Journal of Chemical Physics 12/2004; 121(22):11296-300. · 3.33 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The D" boundary layer between the crystalline silicate mantle and molten
iron core displays the largest contrast in physical and chemical
properties of all the regions in the Earth, and undoubtedly plays a
pivotal role in global dynamics and evolution. Recent high
pressure-temperature (P-T) experiments and ab-initio theoretical
calculations indicate that the pure end-member MgSiO3
transforms to a post-perovskite (ppv) phase with the CaIrO3
structure. Natural olivine with 12 mole percent
Fe2SiO4 and synthetic orthopyroxenes with 20 and
40 percent FeSiO3 were studied at high pressure-temperature
to explore the possible incorporation of iron into ppv. The studies
were conducted at Sector 13 (GSECARS) and 16 (HPCAT) of the Advanced
Photon Source, Argonne National Laboratory. Samples were compressed in a
diamond anvil cell and laser-heated. All samples were found to convert
entirely or partially into the ppv structure, which was recently
reported for pure MgSiO3. With the liquid core as an
unlimited reservoir of iron, core-mantle reactions could further enrich
the iron content in this phase and explain the intriguing seismic
signatures observed in the D" layer.
AGU Fall Meeting Abstracts. 11/2004; -1:05.
-
[show abstract]
[hide abstract]
ABSTRACT: We have performed in situ x-ray and neutron-diffraction measurements, and molecular dynamics simulations, of GeO2, an archetypal network-forming glass under pressure. Below 5 GPa, additional atoms encroaching on the first tetrahedral shell are seen to be a precursor of local coordination change. Between 6 and 10 GPa, we observe structures with a constant average coordination of approximately 5, indicating a new metastable, intermediate form of the glass. At 15 GPa, the structure of a fully octahedral glass has been measured. This structure is not retained upon decompression and, therefore, must be studied in situ.
Physical Review Letters 10/2004; 93(11):115502. · 7.37 Impact Factor
-
Wendy L Mao,
Wolfgang Sturhahn,
Dion L Heinz,
Ho-Kwang Mao,
Jinfu Shu,
Russell J Hemley,
W Sturhahn,
D L Heinz,
H.-K Mao,
J Shu, R J Hemley
[show abstract]
[hide abstract]
ABSTRACT: We studied the nuclear resonant x-ray scattering of iron hydride (FeH x) up to 52 GPa. Coupled with hydrostatic x-ray diffraction data, the partial phonon density of states measured by nuclear resonant inelastic x-ray scattering provides information on sound velocities and the Fe contribution to thermodynamic parameters. In particular it constrains the aggregate shear velocity and shear modulus for comparison to seismic observations. We found that VS (km/sec) = 0.023*P (GPa) + 3.2. A loss of magnetism was observed with synchrotron Mössbauer spectroscopy at 22 GPa, lower than theoretically predicted but consistent with the observed anomalous velocity behavior. Results confirm that FeH x could be a major light element bearing phase for explaining the core density deficit relative to pure Fe. Formation of FeH x by reaction with water would be expected to leave a signature in the mantle.
Geophysical Research Letters 08/2004; 31. · 3.79 Impact Factor
-
Jung-Fu Lin,
Wolfgang Sturhahn,
Jiyong Zhao,
Guoyin Shen,
Ho-Kwang Mao,
Russell J Hemley,
J.-F Lin,
W Sturhahn,
J Zhao,
G Shen,
H Mao, R J Hemley
[show abstract]
[hide abstract]
ABSTRACT: The laser-heated diamond anvil cell has been widely used to study mineral physics under high pressure and temperature, and these studies have provided valuable information in understanding planetary interiors; however, use of the spectroradiometric method in the studies has raised concerns about the accuracy of obtained temperature values. We have built a laser-heating system coupled with nuclear resonant inelastic x-ray scattering to explore particular physical properties of deep-Earth materials. Energy spectra of iron were measured up to 58 GPa and 1700 K. The detailed balance principle applied to the inelastic x-ray scattering spectra provides absolute temperatures of the laser-heated sample. These temperatures are in very good agreement with values determined from the thermal radiation spectra fitted to the Planck radiation function up to 1700 K. Our data provide, for the first time, independent confirmation of the validity of temperatures determined from spectroradiometric method in the laser-heated diamond cell experiments.
Geophysical Research Letters 07/2004; 31. · 3.79 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The high-pressure behavior of nitrogen in NaN(3) was studied to 160 GPa at 120-3300 K using Raman spectroscopy, electrical conductivity, laser heating, and shear deformation methods. Nitrogen in sodium azide is in a molecularlike form; azide ions N(3-) are straight chains of three atoms linked with covalent bonds and weakly interact with each other. By application of high pressures we strongly increased interaction between ions. We found that at pressures above 19 GPa a new phase appeared, indicating a strong coupling between the azide ions. Another transformation occurs at about 50 GPa, accompanied by the appearance of new Raman peaks and a darkening of the sample. With increasing pressure, the sample becomes completely opaque above 120 GPa, and the azide molecular vibron disappears, evidencing completion of the transformation to a nonmolecular nitrogen state with amorphouslike structure which crystallizes after laser heating up to 3300 K. Laser heating and the application of shear stress accelerates the transformation and causes the transformations to occur at lower pressures. These changes can be interpreted in terms of a transformation of the azide ions to larger nitrogen clusters and then polymeric nitrogen net. The polymeric forms can be preserved on decompression in the diamond anvil cell but transform back to the starting azide and other new phases under ambient conditions.
The Journal of Chemical Physics 07/2004; 120(22):10618-23. · 3.33 Impact Factor
-
Jung-Fu Lin,
Viktor V Struzhkin,
Wolfgang Sturhahn,
Eugene Huang,
Jiyong Zhao,
Michael Y Hu,
Ercan E Alp,
Ho-Kwang Mao,
Nabil Boctor,
Russell J Hemley,
J.-F Lin,
V V Struzhkin,
W Sturhahn,
E Huang,
J Zhao,
M Y Hu,
E E Alp,
H.-K Mao,
N Boctor, R J Hemley
[show abstract]
[hide abstract]
ABSTRACT: Understanding the alloying effects of nickel and light element(s) on the physical properties of iron under core conditions is crucial for interpreting and constraining geophysical and geochemical models. We have studied two alloys, Fe0.92Ni0.08 and Fe0.85Si0.15 , with nuclear resonant inelastic x-ray scattering up to 106 GPa and 70 GPa, respectively. The sound velocities of the alloys are obtained from the measured partial phonon density of states for 57Fe incorporated in the alloys. Addition of Ni slightly decreases the compression wave velocity and shear wave velocity of Fe under high pressures. Silicon alloyed with Fe increases the compressional wave velocity and shear wave velocity under high pressures, which provides a better match to seismological data of the Earth's core.
Geophysical Research Letters 10/2003; 30:2112-2115. · 3.79 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Room temperature investigations on the shear stress and deformation mechanisms of (Mg0.9Fe0.1)SiO3 perovskite are performed in situ up to 32 GPa using radial X-ray diffraction and the diamond anvil cell as a deformation apparatus. The uniaxial stress supported by the perovskite aggregate is found to increase continuously with pressure up to 10.9(±1.9) GPa at 32(±1) GPa. Our measurements show no development of significant lattice preferred orientations in the sample, which indicates that deformation by dislocation glide is not the dominant deformation mechanism under these conditions. Assuming that the underlying cause for seismic anisotropy in the deep Earth is elastic anisotropy combined with lattice preferred orientation, our results indicate that silicate perovskite deformed under the conditions of this experiment would not be the source of seismic anisotropy.
Earth Planet. Sci. Lett. 01/2003; 209:351-360.
-
Earth and Planetary Science Letters 01/2003; 209(3-4):351-360. · 4.18 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Synchrotron x-ray diffraction (XRD) and infrared (IR) absorption spectra of hydrous and 'anhydrous' forms of phase X were measured to 30 GPa at room temperature. Three OH stretching modes were found in the hydrous phase, and surprisingly one sharp OH mode was observed in the previously characterized anhydrous phase. All OH stretching modes soften and broaden with increasing pressure and become very weak above ~20 GPa. XRD indicates that the crystal structure remains stable up to 30 GPa. Combining IR absorption and XRD results, the behaviour is attributed to pressure-induced distortion of the Si2O7 groups and disorder of the hydrogen atoms. The bulk moduli of the hydrous and 'anhydrous' phases are in the region of 74 GPa.
Journal of Physics Condensed Matter 10/2002; 14(44):10641. · 2.55 Impact Factor
