The equation of state of osmium at High P,T: a Metal Analog of Fe in the Earth's Core |
| Matt M Armentrout UCLA armentrout@ucla.edu Abby Kavner |
| Facility: APS-GSECARS Format: Poster |
| The transition metal osmium can be considered as a material analog for the high pressure behavior of the primary core metal iron since it is in the same group but has higher electron density. Additionally a number of ultrahard materials are synthesized using osmium; hence its properties are of interest as a baseline for comparison. We examined the phase stability, density, and thermoelasticity of osmium metal at pressures up to 50 GPa, and temperatures up to 2900 K in the laser-heated diamond anvil cell in conjunction with X-ray diffraction at two synchrotron facilities and different experimental conditions. At beamline 12.2.2 at the Advanced Light Source we used NaCl as a thermal insulator and internal pressure marker. At GSECARS at the Advanced Photon Source we used ruby and MgO as pressure standards and neon gas to provide a more hydrostatic environment. We find good agreement between the two data sets despite different facilities and pressure standards. Our data show that osmium is stable in the hexagonal-close-pack phase throughout the study. At room temperature we find an isothermal bulk and a first pressure derivative consistent with literature values. We also find that the c/a ratio of the osmium unit cell increases with both pressure and temperature towards the ideal value of 1.633. Potential sources of error in the thermoelasticity measurements will be discussed in terms of thermal pressure in the laser-heated diamond anvil cell, calibration of pressure across multiple standards, and temperature measurement. The implications in terms of structure and thermoelasticity of Earth's core will be discussed. |
Enhanced convection and fast plumes in the lower mantle induced by the spin transition in ferropericlase. |
| Dan J Bower Seismological Laboratory, California Institute of Technology, Pasadena, California, USA. danb@gps.caltech.edu Michael Gurnis and Jennifer M. Jackson. Seismological Laboratory, California Institute of Technology, Pasadena, California, USA. Wolfgang Sturhahn. Advanced Photon Source, Argonne National Laboratory, Lemont, Illinois, USA. |
| Facility: None Format: Poster |
| Using a numerical model we explore the consequences of the intrinsic density change (Dr/r ~ 2 ? 4%) caused by the Fe2+ spin transition in ferropericlase on the style and vigor of mantle convection. The effective Clapeyron slope of the transition from high to low spin is strongly positive in pressure-temperature space and broadens with high temperature. This introduces a net spin-state driving density difference for both upwellings and downwellings. In 2-D cylindrical geometry spin-buoyancy dominantly enhances the positive thermal buoyancy of plumes. Although the additional buoyancy does not fundamentally alter large-scale dynamics, the Nusselt number increases by 5 ? 10%, and vertical velocities by 10? 40% in the lower mantle. Advective heat transport is more effective and temperatures in the core-mantle boundary region are reduced by up to 12%. Our findings are relevant to the stability of lowermost mantle structures. |
Molybdenum High Pressure Metal-Silicate Partitioning Behavior |
| Laura K Burkemper University of New Mexico burkeml@unm.edu Carl B. Agee |
| Facility: Other Format: Poster |
| The moderately siderophile elements can be used to constrain core formation models by examining their metal-silicate partitioning behavior. Compared to the other moderately siderophile elements (i.e. Ni and Co) there is a paucity of partitioning data for Mo. We have calculated 50+ Mo partition coefficients, D(Mo), from previously published melt property experimental data collected in our lab and performed 20+ new partitioning experiments; therefore greatly increasing the Mo partitioning data-set found in the literature. We preformed experiments in a Walker-type multi-anvil press over the temperature range of 1435-2100 oC and pressure range of 2.5-11 GPa. We determined that temperature and pressure have little effect on D(Mo) over the ranges that we examined. However, composition was found to have a much stronger effect on D(Mo). Our starting materials consisted of powders with a very high NBO/T value (synthetic KLB-1) to those with very low NBO/T values (natural basalt) allowing us to thoroughly examine the effect of silicate composition. Two high-Ti synthetic materials were also used to investigate the role of Ti in silicate melts. Our preliminary results show that titanium seems to act like a tetrahedrally coordinated cation (similar to silicon) and D(Mo) decreases by an order of magnitude with increasing NBO/T. This result makes sense because Mo is a high valence cation and therefore D(Mo) should be sensitive to changes in silicate composition. Additionally, the effect of oxygen fugacity was examined and D(Mo) was found to decrease with increasing oxygen fugacity. Our data shows that Mo is more sensitive to changes in composition and oxygen fugacity than pressure and temperature This implies that the high valence cations, like Mo, will be extremely useful for constraining the silicate composition and oxygen fugacity conditions of the early differentiating Earth. |
Elastic Plastic Self Consistent (EPSC) Modeling of Plastic Deformation in Fayalite Olivine |
| Pamela C Burnley University of Nevada, Las Vegas burnley@physics.unlv.edu Mike Brawner Greg Hoth Sergio Dieguez Alex Drue John Boisvert Milos Visekruna |
| Facility: NSLS-X17B2 (MAC) Format: Poster |
| We report on in-situ synchrotron x-ray diffraction from high pressure deformation experiments conducted using fayalite. The experiments were conducted using the D-DIA apparatus at beamline X17b2 at the NSLS. We observe the diffraction behavior of x-ray reflections for lattice planes oriented nearly perpendicular to compression and at several other orientations including the transverse orientation which contains the compression direction. Sample strain is measured by periodically taking a radiograph of the sample (which is bounded by metal foils) and comparing the length of the sample to a radiograph taken immediately before the start of the deformation experiment. We used elastic plastic self consistent (EPSC) modeling to analyze diffraction from the sample during deformation. Our EPSC models of olivine indicate that the operation of various slip systems impacts in-situ diffraction in different ways. Although there are broad similarities, the operation of most of the olivine slip systems gives a distinctive signature in the ordering of the diffracted peaks. This is augmented by the fact that the effect of slip on diffraction for planes oriented perpendicular to the compression direction and those containing the compression direction are not related in a simple or consistent way for all slip systems and thus contain additional information. In the EPSC models, the failure of the known olivine slip systems to meet the von Mesis criteria for arbitrary shape change results in very strong work hardening and nearly elastic behavior for many grain populations. This is in stark contrast to our experimental data which consistently shows little or no work hardening after yield. The failure of the EPSC models to be able to reproduce the behavior of fayalite olivine highlights the role of the accommodation mechanism (which is not considered in the EPSC model) in determining the strength of olivine during plastic deformation. |
Melting experiments at high pressures |
| Andrew Campbell University of Maryland ajc@umd.edu Noah A. Miller Rebecca A. Fischer (also at Northwestern University) E. Tess Van Orden |
| Facility: APS-GSECARS Format: Poster |
| Melting and crystallization processes are responsible for most of the large scale differentiation in the Earth and other planets, so it is important to establish melting curves and phase diagrams to high pressure conditions. However, significant discrepancies remain in the recent literature, even for relatively simple phases and those that are very important to planetary interiors; therefore it is useful to have multiple experimental tools to investigate high pressure melting processes. Our present work is based on a recently developed method for measuring 2D temperature distributions in laser heated diamond anvil cell samples, and exploits changes in these temperature distributions and their relation to the apparent emissivity of the sample and (in some cases) laser power. We show melting curves in wustite, Fe-Si alloys, and Mo as examples of the method. Comparison of these results to our recent synchrotron XRD-based melting studies show that those measurements tend to slightly overestimate the melting temperature, if the axial temperature gradient through the sample is not explicitly accounted. |
Change in the Equation of State of Mg-silicate Perovskite by Fe3+ Spin Transition and Fe-Al Site Mixing |
| Krystle C Catalli Massachusetts Institute of Technology krystle@mit.edu S.-H. Shim (MIT) P. Dera and V. B. Prakapenka (GSECARS) J. Zhao and W. Sturhahn (APS, XOR-3) P. Chow and Y. Xiao (HPCAT) H. Cynn and W. J. Evans (LLNL) |
| Facility: Other Format: Poster |
| Although recent studies have shown that the Fe spin transition in ferropericlase results in volume contraction at pressures corresponding to the lowermost mantle, existing studies are in disagreement on how the spin transition in Mg-silicate perovskite (Pv) occurs and whether it affects the density of Pv, which represents more than 70% of the lower mantle. Studies have found that the ratio of Fe3+ to Fe2+ in Pv is enhanced due to coupling with Al (50 %), the majority of which enters Pv in the lower mantle [McCammon, 1997, Nature], and that Fe3+ in Pv undergoes a gradual spin transition in the mantle [Catalli et al., 2009, in review]. We have conducted X-ray emission spectroscopy, nuclear forward scattering, and X-ray diffraction on Pv with equal amounts of Fe3+ and Al (10 mol%) to 90 GPa. We found that the population of low spin Fe3+ increases near 70 GPa, from 20% to 60%, reflecting an increase in low spin Fe3+ entering the octahedral site, which means an equal amount of Al must move into the dodecahedral site. This suggests that the similar ionic sizes of low-spin Fe3+ and Al allows mixing between the two diffrerent crystallographic sites in Pv after the spin transition. Fe3+-Al-Pv has a larger volume at lower pressure than Mg-endmember Pv, but its volume approaches that of Mg-endmember near the pressure where the Fe3+-Al site mixing increases, resulting in an elastic softening and contraction of volume. Therefore, Pv should be more compressible and denser in the lowermost mantle than previously thought due to the Fe3+ spin transition and Fe-Al site mixing. This indicates that the density increase in the lowermost mantle found in seismological studies does not necessarily require Fe-enrichment [van der Hilst and Karason, 1999, Science]. Our results may also explain the discrepancy in spin transitions in Al-bearing and Al-free Pv found in previous studies [Badro et al., 2004, Science; Li et al., 2004, PNAS]. |
Equation of state of Fe7C3 up to 1.7 Mbar using single-crystal XRD on laser annealed samples in neon pressure medium |
| Bin Chen University of Illinois at Urbana-Champaign binchen2@uiuc.edu Mike Frothingham Lili Gao Barbara Lavina (GSECARS, University of Chicago) Przemyslaw Dera (GSECARS, University of Chicago) Vitali B. Prakapenka (GSECARS, University of Chicago) Jie Li |
| Facility: APS-GSECARS Format: Poster |
| Carbon is among the leading candidates for the principal light element in the Earth?s iron-rich core. Testing the hypothesis of a carbide-rich inner core requires accurate knowledge of the phase stability and equation-of-state of the relevant phases under core conditions. Recent studies suggest that Fe7C3, is a potential component in the solid inner core [Wood et al., 1993 EPSL; Nakajima et al.,2009 PEPI; Lord et al. 2008 AGU]. We have collected single-crystal x-ray diffraction data of Fe7C3 in neon pressure medium up to 1.7 Mbar at room temperature at 13 BM-D and 13-ID-D of GSECARS using the method described in Dera et al. [2008]. Fe7C3 was synthesized from iron rod in a graphite capsule using a large-volume press at University of Illinois. Single crystals were selected at 13-BM-C of GSECARS. The GSE-ADA and RSV software by P. Dera [2007] was used for three-dimensional reconstruction of reciprocal space, peak indexing and fitting. Our results of phase stability and equation-of-state of Fe7C3 are applied to test models of carbon-rich core. |
Density determinations usding High Pressure X-ray Microtomography |
| Alisha N Clark Department of Geology, University of California, Davis, CA 95616, USA anclark@ucdavis.edu Dr. Charles E. Lesher Sarah Gaudio Dr. Yanbin Wang (GeoSCoilEnvironCARS, Center for Advanced Radiation Sources, Univ. Chicago, Chicago, Il 60637, USA) |
| Facility: APS-GSECARS Format: Poster |
| The density of silicate glasses and melts are being determined by high pressure X-ray microtomography (HPXMT) using the rotating anvil apparatus (RAA) on the 13-BM-D beamline at the Advanced Photon Source at Argonne National Laboratory. The RAA consists of two opposing HarmonicDrive? motor driven by precision stepper motors mounted to a die set and compressed with a 250-ton press. Stepper motors advance the harmonic drives in unison for tomographic data collection. Sample are placed between opposing anvils of a Drickamer cell, consisting of a composite gasket of boron epoxy and fired pyrophyllite ± diamond epoxy surrounded by a containment ring of polytherimide plastic, and compressed by the coupler plates loaded through the die set by the hydraulic press. The utility of HPXMT is demonstrated for two silicate compositions. The density of SiO2 glass is determined up to 3.5 GPa at room temperature by volume rendering and is compared to our previous measurements on MgO-rich silicate glasses. We also report new results of heating basalt glass (BCR-2) up to 900 ºC at 1 GPa where density is determined by X-ray absorption. Further developments are underway to extend these latter measurements into the melting interval for basalt and pressures up to 10 GPa. |
Influence of the crystal field effect on chemical transport in Earth's mantle: Cr3+ and Ga3+ diffusion in periclase |
| Katherine L Crispin Case Western Reserve University, Department of Geological Sciences, Cleveland, OH 44106-7216 katherine.crispin@case.edu James A Van Orman |
| Facility: Other Format: Poster |
| Trivalent impurities govern cation vacancy concentrations in most minerals, and thus play a central role in solid-state diffusion in the Earth. Although periclase is among the simplest of minerals, diffusion of trivalent cations is a complex process. Trivalent cations tend to bind to oppositely charged cation vacancies to form highly mobile pairs; the continual presence of a vacancy adjacent to the trivalent impurity allows it to move through the lattice much more rapidly than it would in the absence of binding. Diffusion experiments were performed to determine the mobility and binding energy of Cr3+- and Ga3+-vacancy pairs. Cr3+ and Ga3+ have almost identical ionic radii and polarizability, yet these experiments show that Ga3+ diffuses more than an order of magnitude faster than Cr3+, has a lower activation energy, and binds more tightly to the adjacent vacancy. All of these observations can be explained by the crystal field stabilization of Cr3+ on octahedral cation sites in MgO. Cr3+ contains only three d-orbital electrons whereas the 3d-shell of Ga3+ is full. This partial filling of the d-orbitals leads to a lowering of energy; the three d-electrons of Cr3+ occupy t2g orbitals that experience less repulsive interaction with the electrons of the six surrounding oxygen atoms. This crystal field stabilization increases the activation energy for Cr3+ migration to an adjacent vacancy. It also may explain the lower binding energy of vacancies to Cr3+. The crystal field stabilization is greatest for perfect octahedral symmetry; there is an energy cost associated with the presence of an adjacent symmetry-breaking vacancy, and consequently a reduction in the binding energy. The crystal field effect has long been known to influence the partitioning of first-row transition metals in minerals, but its influence on diffusion has not previously been considered. Our experimental results indicate that the crystal field effect may have an even stronger influence on diffusion rates than it does on partitioning. |
Analysis of deformation mechanisms through grain-size study of polycrystalline olivine in the D-DIA |
| Nathaniel A Dixon Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology dixonn@mit.edu William B. Durham Ayako Suzuki: Department of Geology and Geophysics, University of Minnesota, Twin Cities Shenghua Mei: Department of Geology and Geophysics, University of Minnesota, Twin Cities David L. Kohlstedt: Department of Geology and Geophysics, University of Minnesota, Twin Cities |
| Facility: NSLS-X17B2 (MAC) Format: Poster |
| The D-DIA apparatus was used to deform dry polycrystalline olivine in a dual sample cell with two distinct uniform grain sizes. The cell was designed such that the stress and temperature conditions for both the large grained (~60 µm) and fine grained (~5 µm) olivine were near identical. The samples were deformed at temperatures of ~1573 K and a constant strain rate of about 4 · 10^-6 s^-1 to over 30% strain. Deformation was observed in situ during the experiments with the use of strain markers placed at the sample margins, visible in x-radiographs. At the same time, elastic strain was measured in both halves of the sample assembly (fine and coarse), with the use of synchrotron x-ray diffraction and new variable-width collimating slits. This allowed comparison of stresses between sample halves at much higher resolution than in previous D-DIA experiments, and confirmed similar stress states. Both grain sizes deformed to similar strains, the fine-grained sample deforming only slightly faster than its coarse counterpart. This is consistent with expectations for deformation with a large component of dislocation creep, and suggests a much smaller role of diffusion creep or diffusion-assisted grain boundary sliding at these test conditions. Post-experiment SEM images showed that grain size in the initially coarse samples had significantly decreased during deformation. |
Pyrope-grossular Thermoelasticity |
| Wei Du Columbia University in the City of New York weidu@ldeo.columbia.edu Dave Walker Columbia University in the City of New York Simon Clark£¬Martin Kunz£¬ Wendel A. Caldwell Advanced Light Source, Lawrence Berkeley National Laboratory |
| Facility: NSLS-U2A (DAC) Format: Poster |
| Unit-cell volumes of Multi-anvil synthesized single-phase intermediate pyrope-grossular solid solutions have been mea¬sured by XRD to pressures and temperatures of ~70 kbar and ~600 ¡ãC. The pyrope-gossular garnet series has larger excess volumes than those literature data from piston/cylinder synthesis, and smaller than garnets synthesized from diamond anvil cells. Intermediate garnets show excess volumes approaching 0.9cm3/mol, which are ~3 times those previously reported. The excess volume pattern at room temperature is asymmetric leaning toward grossular. A two-parameter Margules equation fitted to the data gives = 4.90.7 cm3/mol, = 1.10.8 cm3/mol at 298K, showing the same sense of asymmetry as Boseneck and Geiger¡¯s (1997) study but are ~3 times larger. Thermal expansions of garnets in this series range from 1.9-3.0e-5/K and uniformly increase with temparture at rates that differ with garnet composition. The values for endmembers pyrope and grossular closely follow those given by Skinner (1956). Birch-Murnaghan EOS has been used to fit the P-V data to determine the bulk moduli of these garnet samples. For the endmember grossular and pyrope, the Birch-Murnaghan EOS yields K0=165.4(1.5) GPa and K0=173.5(3.0) GPa, respectively, where K0¡¯ are fixed to be 5.92 (Pavese et al, 2001). The elastic properties here reported are comparable with previous report. |
Transformation Kinetics of Olivine containing 88 ppm of H2O |
| Wyatt L Du Frane Arizona State University wd@asu.edu Thomas G. Sharp, Arizona State University Jed Mosenfelder, California Institute of Technology Kurt Leinenweber, Arizona State University |
| Facility: Other Format: Poster |
| Hydrogen increases the growth rate of olivine transformation into ringwoodite by aiding the diffusion of ions across the growth interface and by hydrolytic weakening of the growth rim. The rate olivine transforms into ringwoodite determines the likelihood that metastable olivine persists into the Earth?s mantle transition zone as a wedge in subducting slabs. Transformational faulting of metastable olivine has been proposed as a triggering mechanism for deep earthquakes, and seismic low velocity zones that coincide with the observed locations of deep earthquake hypocenters have been interpreted to be metastable olivine in subducted slabs. However it is believed that downwelling slabs are hydrated by the breakdown of serpentine, and previous results have indicated that olivine containing as little as 290 wt-ppm D2O (an H2O proxy) will transform too quickly for a metastable wedge of olivine to survive into the Earth?s transition zone. We present olivine-ringwoodite transformation kinetics using olivine hydrated in a piston cylinder with 88 ppm of H2O, determined using FTIR. We have previously reported hydrogen contents of ~30 ppm H2O in our samples, however the SIMS calibration used to calculate these measurements underestimated hydrogen content; the FTIR measurements of hydrogen content in our samples are in line with previous studies on hydrogen solubility in olivine. Some of our previous results may have been subjected to hydrogen contamination; we have changed our procedure to solve this problem. Nominally anhydrous olivine growth rates obtained by this new procedure are lower and compare favorably to nominally anhydrous olivine growth rates by Diedrich, et al., [2009]. Growth rates of olivine containing 88 ppm of H2O, 3.80x10^-8 m/s at 18 GPa and 1100 ◦C, are rapid in comparison to those of nominally anhydrous olivine, 3.7 x 10^-9 m/s s at 18 GPa and 1100 ◦C. The activation enthalpy for ringwoodite growth in olivine with 88 ppm H2O (187 kJ/mol) is comparable to growth rates of 290 ppm D2O samples (232 kJ/mol) by Diedrich, et al., [2009]. The similarity of growth rates for olivine containing 88 ppm of H2O (with and without hydrogen contamination) and olivine with 289 ppm of D2O suggest that a small amount of hydrogen goes a long way in enhancing olivine growth rates, primarily by hydrolytic weakening of the growth rim for these low hydrogen contents. Based on the thermo-kinetic models by Diedrich, et al. [2009], 88 ppm H2O in olivine within old, cold, and fast subducting slabs would eliminate the metastable wedge of olivine. Consequently if slabs contain metastable olivine at transition zone depths, the olivine must have less than 88 ppm H2O. |
Early Lunar Magma Ocean Cumulates as Possible Source Lithologies for the Mg ? Suite |
| Stephen M Elardo Institute of Meteoritics, University of New Mexico selardo@unm.edu David S. Draper |
| Facility: Other Format: Poster |
| Though the petrogenesis of magnesium and rare earth element ? rich plutonic lithologies on the Moon (typically termed the Mg ? suite) has remained enigmatic, early cumulates produced in the Lunar Magma Ocean (LMO) have been postulated as potential source lithologies. Olivine ? orthopyroxene cumulates may have been brought to shallower depths by cumulate overturn, where partial melts of these lithologies assimilated some portion of KREEP, the late stage incompatible element enriched residual LMO liquid. We have conducted equilibrium crystallization experiments from 0.5 to 4.5 GPa on the Taylor Whole Moon (TWM) composition to simulate crystallization in the LMO and determine the composition of the first mafic cumulates. This composition represents a Moon enriched in refractory elements (e.g. Al, Th) by 50% relative to Earth. Highly magnesian olivine (Fo 95 ? 97) is the liquidus phase at all Moon relevant pressures and is followed in the crystallization sequence by low ? Ca pyroxene (En 93 ? 95). The compositions of these minerals do not vary significantly with pressure. High ? Ca pyroxene does not join the crystalline assemblage until relatively late in the crystallization sequence and although it is present as the only pyroxene in the sub-solidus assemblage at 4.5 GPa (along with olivine and garnet), it is generally believed, on the basis of major and trace element geochemistry, that the Mg ? suite did not form from a partial melt of a high ? Ca pyroxene and garnet bearing source lithology. However, olivine ? orthopyroxene cumulates similar in composition to those produced in our experiments have been hypothesized by various authors to be the source rocks of the Mg ? suite. Therefore, our experiments suggest that the earliest formed cumulates produced at any depth in a TWM composition LMO could potentially serve as the source lithologies for the Mg ? suite plutonic rocks. |
Anisotropy in sound velocities of Fe3C with implications for Earth?s core |
| Lili Gao Department of Geology, University of Illinois at Urbana-Champaign; Advanced Phonon Source (APS), Arg liligao2@uiuc.edu Bin Chen Wolfgang Sturhahn Ercan E. Alp Jiyong Zhao Jie Li |
| Facility: Other Format: Poster |
| We carried out nuclear resonant inelastic X-ray scattering (NRIXS) measurements on a textured 57Fe3C sample composed of a few crystals [Gao et al., 2008] and a powder 57Fe3C sample [Gao et al., accepted]. Partial phonon density of states (PDoS) of iron in Fe3C were extracted from our NRIXS spectra. Combining the PDoS with an existing equation of state of Fe3C [Scott et al., 2001], we derived the compressional wave velocities (Vp) and shear wave velocities (Vs) of Fe3C. Our results at ambient conditions show that the textured and powder samples have distinct Vp and VS, indicating strong anisotropy in Fe3C. These results are consistent with a recent report of extreme elastic anisotropy in Fe3C on the basis of first-principle calculations and X-ray diffraction measurements [Nikolussi et al., 2008]. Anisotropy in Fe3C may be partially responsible for the seismically observed anisotropy in the Earth?s inner core [e.g. Morelli et al., 1986; Sun and Song, 2008]. References: Gao, L. et al. (2008) Geophys. Res. Lett., 35:L17306 doi:10.1029/2008GL034817. Gao, L. et al. J. Synchrotron Radiat. (accepted). Morelli, A and A. M. Dziewonski (1986) Geophys. Res. Lett., 13, 1545-1548. Scott, H. P. et al. (2001), Geophys. Res. Lett., 28, 1875-1878. Nikolussi, M. et al. (2008) Scr. Metall., 59 814-817. Sun, X. and Song, X. (2008) Earth and Planet. Science Let., 269, 56?65. |
Structural relaxation phenomena in amorphous silicates at high pressure and temperature |
| Sarah J Gaudio Department of Geology, University of California, Davis, California, U.S.A. Gaudio@geology.ucdavis.edu Charles E. Lesher Sabyasachi Sen Department of Chemical Engineering and Materials Science, University of California, Davis, California, U.S.A. |
| Facility: None Format: Poster |
| Relaxation phenomena in vitreous NaAlSi3O8 and vitreous MgSiO3, strong and fragile compositions respectively, are explored by comparing the densities of glasses recovered from high pressure (up to 8.5 GPa) and a range of temperatures across the glass transition interval (Tg). Our method is to heat treat glass samples at high pressure over the relaxation timescale of 300 seconds and then measure the recovered density by Archimedes? method. Because we are relaxing glasses at Tg and sub-Tg conditions, our experiments are fundamentally different from traditional melt-quench methods where glasses are rapidly quenched from superliquidus conditions that typically results in high fictive temperatures (Tf). In addition to measuring the density of recovered glasses, structural relaxation is monitored by measuring the proportion of high-coordinated aluminum by 27Al magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Both strong and fragile glasses begin structural relaxation at temperatures hundreds of degrees below the Tg interval. Strong compositions (vitreous NaAlSi3O8) can be fully equilibrated at and above Tg, while fragile compositions experience the onset of crystallization over the 300-second timescale. Moreover, the pressure dependence of sub-Tg viscosities is estimated by measuring the rate of density relaxation at various P-T conditions. This approach is being utilized to determine the fragility of supercooled liquids at high pressures. |
Diamond Anvil Cell X-Ray Diffraction Facilities at NSLS, Brookhaven National Laboratory |
| Sanjit K Ghose Mineral Physics Institute, Stony Brook University, Stony Brook, NY ghose@cars.uchicago.edu Zhiqiang Chen, Lars Ehm, Donald Weidner Mineral Physics Institute, Stony Brook University, Stony Brook, NY Thomas Duffy Department of Geosciences, Princeton University, Princeton, NJ |
| Facility: NSLS-X17C (DAC) Format: Poster |
| The diamond anvil cell X-ray (X17-DAC) facilities at the National Synchrotron Light Source (NSLS) were the first dedicated high-pressure beam lines in the world, and has been a workhorse for diamond anvil cell research for more than two decades. The X17-DAC facilities are located on a superconducting wiggler beam line and consist of two stations (X17C and X17B3) together with a sample preparation/spectroscopy laboratory. Both X17C and X17B3 beam lines are available for energy dispersive (EDXD) and monochromatic (ADXD) experiments. At both the beam lines monochromatic beams are available at lower dimension (10-20 micron) and higher flux through Sagittally-bent double Si crystal Laue mode (transmission) monochromator, in conjunction with a K-B mirror. X17C beam line with both focused white beam and monochromatic beam (30KeV) provides the capabilities of diffraction at extreme condition of pressure and temperature from powder, single crystal and nanocrystal samples. At X17B3 in addition to the EDXD capability two different energy ranges of monochromatic beams are available at 30 keV and 80 keV for achieving Angle Dispersive Diffraction up to a very high Q range to get data for a total scattering geometry. These capabilities are unique in terms of X-ray diffraction data collection at high Q range and higher flux. |
Effect of water in high pressure and high temperature deformation of olivine single crystal |
| Jennifer A Girard CeSMEC, Florida International University, University Park Campus, Blg. VH140, Miami, Florida 33199, jennifer.girard@hotmail.fr Jiuhua CHEN1, Paul RATERRON2, Caleb HOLYOKE3 1, CeSMEC, Florida International University, University Park Campus, Blg. VH140, Miami, Florida 33199, USA 2,LSPES, CNRS, Bat C6, Universite des Sciences et Technologies de Lille, Villeneuve d'Ascq F-59655, France 3, Department of Geology and Geophysics, MS 3115, Texas A&M University, College Station, Texas |
| Facility: NSLS-X17B2 (MAC) Format: Poster |
| Seismic velocity anisotropies observed in the upper mantle are interpreted from lattice-preferred orientations (LPO) produced experimentally in olivine, which depends on the dominant dislocation slip systems. At low pressure P <3GPa, mantle temperature (T) and in dry conditions, olivine [100] dislocation slip dominates the less active [001] slip. This tends to align crystal fast velocity [100] axis with the principal shear direction. Yet recent high-pressure deformation experiments [1] show that [001](010) slip system dominates [100](010) system in the (P,T) range of the deep upper mantle. This may promote a shear-parallel slow-velocity [001] axis and may explain the seismic-velocity attenuation observed at depth >200 km [2]. However the water contains in the sample can have an influence on the slip system activation. In fact, previous study revealed that at high temperature and pressure the water could affect the olivine plastic deformation and induce the transition between the [100] slip to the [001] slip. [3] In order to show the effect of water on olivine slip system activities at high pressure, deformation experiments were carried out in wet and dry condition, at P<8 GPa and T=1200\degC, on pure Forsterite (Fo100) and San Carlos olivine crystals, using the Deformation-DIA apparatus at the X17B2 beamline of the NSLS (Upton, NY). To keep the water in the cell assembly during the high-pressure deformation experiments, a sleeve of talc was placed in the cell, around the single crystal samples. Then crystals were oriented in order to active either [100] slip alone or [001] slip alone in (010) plane, or both [100](001) and [001](100) systems together. Constant applied stress sigma <300 MPa and specimen strain rates were monitored in situ using time-resolved x-ray diffraction and radiography, respectively. References [1] Couvy et al., 2004, EJM; Raterron et al., 2007, Am. Min.; Raterron et al., 2008, Phys. Earth Planet. Int., doi:10.1016/j.pepi.2008.07.026 [2] Mainprice et al., 2005, Nature [3] Jung et al., 2001, J.S.G.; Jung, et al., 2006, science. |
Spin State of Iron and Thermal Conductivity in the Earth?s Lower Mantle |
| Alexander F Goncharov Geohysical Laboratory, Carnegie Institution of Washington goncharov@gl.ciw.edu A. F. Goncharov 1, V. V. Struzhkin 1, J. Montoya 1, S. Kharlamova 1, R. Kundargi 1, J. Siebert 2, J. Badro 2, D. Antonangeli 2, F. J. Ryerson 3, W. Mao 4 1 Geophysical Laboratory, Carnegie Institution of Washington 2 Département de Minéralogie ? IMPMC, Institut de Physique du Globe de Paris 3 Lawrence Livermore National Laboratory 4 Stanford University, CA |
| Facility: None Format: Poster |
| Optical absorption spectra of lower mantle minerals depend critically on composition (including iron oxidation state), structure, and iron spin state. Here we confirm that the presence of ferric iron in ferropericlase is very essential for the optical properties. We also show that perovskite and postperovskite show substantially different optical absorption in near infrared and visible spectral ranges; this may have a profound effect on dynamics the lowermost mantle. Future accurate assessment of a radiative component of the thermal conductivity would require better knowledge of the compositional and structural parameters and also of the iron spin state of the lower mantle materials. We presented preliminary results of measurements of the thermal conductivity of perovskite at 125 GPa. The available data suggest larger than previously estimated value, although the uncertainty is very large. Future accurate experimental measurements of the phonon part of the thermal conductivity of the lower mantle materials will require a number of carefully crafted experiments to determine the thermal conductivity of all the materials used in the DAC experiments under the relevant for the Earth?s mantle conditions. Thin couplers prepared as metallic films deposited on mineral plates should be used in next generation pulsed laser heating experiments, which are currently being in preparation. |
Synchrotron Mossbauer Spectroscopy of Mg0.8Fe0.2SiO3 Perovskite to 70 GPa |
| Brent Grocholski Massachusetts Institute of Technology] b.grocholski@gmail.com |
| Facility: NSLS-U2A (DAC) Format: Poster |
| Synchrotron Mossbauer Spectroscopy of Mg0.8Fe0.2SiO3 Perovskite to 70 GPa Brent Grocholski, Sang-Heon Shim, Jiyong Zhao, Wolfgang Sturhahn, Yuming Xiao, and Paul Chow Synchrotron Mossbauer spectra (SMS) were measured on a total of five sample of Mg0.8Fe0.2SiO3 perovskite (Pv) (57Fe enriched) between 0 and 70 GPa. Three samples contained a thin (2-3 micron) iron foil with natural Fe level to ensure reducing conditions and two samples were loaded without the iron foils. SMS of the starting material confirms iron is in the 2+ oxidation state. X-ray diffraction on the samples synthesized above 37 GPa confirms full conversion to Pv. Our data set in general can be fit using a three site model similar to previous experiments (Jackson et al., 2005, McCammon et al., 2008), with sites that have quadrupole splitting (QS) values that are low (0.5-1 mm/s, either high spin Fe3+ or low spin Fe2+), intermediate (2.5-3.0 mm/s, either high spin Fe2+ or low spin Fe2+) or high (3.5-4.0 mm/s, formerly interpreted as intermediate spin Fe2+) . Our data is best fit with a high QS component above 50 GPa that increases in weight fraction with pressure to 40% at 70 GPa, but also requires a new site with QS of 1.0-1.5 mm/s that has not been previously reported. The low QS component is necessary to fit our data at all pressure above 5 GPa and varies little in value. The weight fraction of this site decreases above 50 GPa from 40% to 25%. The intermediate QS component is necessary at 5-37 GPa, but disappears entirely at 50 GPa. These trends are consistent with previously published results in general, but the changes occur at higher pressures and with much smaller high QS component. Samples containing Fe foil have a lower amount of low QS iron compared to samples without the foil. We used argon as a quasi-hydrostatic pressure medium and directly converted the starting material to perovskite at high pressure (37, 50, and 65 GPa) with laser heating, which is different from previous measurements. These conditions may play important roles for the observed differences with previous works. |
Synchrotron Mossbauer Spectroscopy of Mg0.8Fe0.2SiO3 Perovskite to 70 GPa |
| Brent Grocholski Massachusetts Institute of Technology b.grocholski@gmail.com Sang-Heon Shim (MIT) Jiyong Zhao, Wolfgang Sturhahn, Yuming Xiao, Paul Chow (Argonne National Lab, APS) |
| Facility: APS-HPCAT Format: Poster |
| Synchrotron Mossbauer spectra (SMS) were measured on a total of five sample of Mg0.8Fe0.2SiO3 perovskite (Pv) (57Fe enriched) between 0 and 70 GPa. Three samples contained a thin (2-3 micron) iron foil with natural 57Fe level to ensure reducing conditions and two samples were loaded without the iron foils. SMS of the starting material confirms iron is in the 2+ oxidation state. X-ray diffraction on the samples synthesized above 37 GPa confirms full conversion to Pv. Our data set in general can be fit using a three site model similar to previous experiments (Jackson et al., 2005, McCammon et al., 2008), with sites that have quadrupole splitting (QS) values that are low (0.5-1 mm/s, either high spin Fe3+ or low spin Fe2+), intermediate (2.5-3.0 mm/s, either high spin Fe2+ or low spin Fe2+) or high (3.5-4.0 mm/s, formerly interpreted as intermediate spin Fe2+) . Our data is best fit with a high QS component above 50 GPa that increases in weight fraction with pressure to 40% at 70 GPa, but also requires a new site with QS of 1.0-1.5 mm/s that has not been previously reported. The low QS component is necessary to fit our data at all pressure above 5 GPa and varies little in value. The weight fraction of this site decreases above 50 GPa from 40% to 25%. The intermediate QS component is necessary at 5-37 GPa, but disappears entirely at 50 GPa. These trends are consistent with previously published results in general, but the changes occur at higher pressures and with much smaller high QS component. Samples containing Fe foil have a lower amount of low QS iron compared to samples without the foil. We used argon as a quasi-hydrostatic pressure medium and directly converted the starting material to perovskite at high pressure (37, 50, and 65 GPa) with laser heating, which is different from previous measurements. These conditions may play important roles for the observed differences with previous works. |
A New Style of Mass Transport Between the Lower and Upper Mantle |
| Christine T Houser University of California Santa Cruz cthouser@ucsc.edu Quentin Williams |
| Facility: None Format: Poster |
| We synthesize new lines of observational evidence which reveal a new style of mass transport between the lower and upper mantle that occurs beneath the Pacific region in which warm material accumulates under the western Pacific due to the absence of a ridge system. This flow occurs in a manner unlike plume upwelling alone which differs in that it is more of a thermal than a plume with a lower vigor of upwelling. The western Pacific region is unique on the Earth as it bounded on almost all sides by subduction with a large fraction of the plate at great distances from spreading ridges which allows this warm material to become stably stratified in the upper portions of the mantle. The new lines of seismic evidence for this new style of transport are the recognition of broad slow shear velocities under the western Pacific extending from 300-1000 km depth, a thin transition zone beneath the western Pacific, and a narrow slow shear velocity column extending from 1000-2200 km depth. These observations coupled with the anomalously low elastic shear wave speeds at the CMB and the concentration of seamounts at the surface provide a means for relating the deepest mantle structure to the enhanced volcanism observed on the Pacific plate. Therefore, the region occupied by the Pacific plate may dominate the heat transfer from the Earth's interior that is not directly associated with plate boundary processes, and that this enhanced heat transport is a direct consequence of the deep underlying structure of the Pacific Basin. |
Shear Deformation of Wadsleyite in the Rotational Drickamer Apparatus |
| Justin W Hustoft Yale University justin.hustoft@yale.edu Takaaki Kawazoe, Zhicheng Jing, Kazuhiko Otsuka, Tomohiro Ohuchi, George Amulele, Zhixue Du, and Shun-ichiro Karato (Yale University), Liping Wang and Michael Vaughan (SUNY Stony Brook) |
| Facility: NSLS-X17B2 (MAC) Format: Poster |
| We have performed shear deformation experiments on samples of polycrystalline wadsleyite at 13-18 GPa and 1300-1800 K in the rotational Drickamer apparatus. Our goal is to collect quantitative data on the rheological properties of wadsleyite at transition zone conditions. Our experiments build on and extend the results of Nishihara et al. (2008) and Kawazoe et al. (2009) on deformation of olivine and wadsleyite. The starting material, San Carlos olivine, was the same as in the previous studies, but had a smaller initial grain size ( <2 micrometers). Wadsleyite was synthesized from this fine-grained olivine in a Kawai-type multianvil; the initial average grain size of the wadsleyite was approximately 1 micrometer. The initial water content of the undeformed wadsleyite was determined to be dry. Deformation experiments were conducted at the X17B2 beamline of the National Synchrotron Light Source, using white x-rays to collect energy-dispersive diffraction patterns at a fixed 2theta of 6.7° over ten azimuth angles. X-ray diffraction spectra were collected in 900 s exposures over the course of each experiment. In situ determinations of strain were made from radiographs of the sample using a Mo foil inserted into the sample assembly as a strain marker. Uniaxial and shear stresses were determined from the observed d-spacing of multiple wadsleyite lattice planes as a function of azimuth angle, utilizing the theory of Singh (1993). Samples of wadsleyite were deformed at three different constant anvil rotation rates, corresponding to strain rates of approximately 10-4 - 10-5 s-1, in an effort to determine the stress exponent. The rotation rate was held constant until steady-state creep was believed to have been reached. Experiments were also conducted at three different constant furnace power conditions, corresponding to temperatures from 1300 to 1800 K. |
A modified hard-sphere model for the compression of silicate liquids |
| Zhicheng Jing Department of Geology and Geophysics, Yale University zhicheng.jing@yale.edu Shun-ichiro Karato |
| Facility: None Format: Poster |
| Compressional properties of silicate liquids are important for our understanding of evolution and dynamics of Earth. Experimental observations have shown that silicate liquids are much more compressible than solids, making liquids denser than solids in the Earth?s deep mantle. However, the compression mechanisms of silicate liquids are still not well understood. In general, equation of state of a material can be obtained by taking the volume derivative of the Helmholtz free energy. For a solid, free energy has two contributions, the potential energy of a static lattice, and the vibrational free energy (thermal contribution). Thus bulk modulus (the second derivative of free energy) of a solid at T=0 K is mostly determined by the potential energy, while the vibrational part gives the temperature dependence. However, under compression atoms in a liquid can undergo structural rearrangement in addition to the uniform shortening of interatomic distances. Therefore another term, the configurational contribution, must be included in the liquid free energy. It is this contribution that leads to the different compression mechanism for liquids. By comparing compressional behaviors of solids, glasses, and liquids for several silicate compositions, we find that glasses and solids have similar bulk modulus-molar volume relationships, while liquids are different. This indicates that the compression mechanisms for glasses and solids are essentially the same. The differences in bulk modulus between solids and glasses can be mainly accounted for by the differences in the molar volume (Birch?s law). However, the bulk moduli of liquids are much smaller than those calculated from the bulk modulus-molar volume relationship for glasses or solids. We find that the additional compression mechanism of liquids is likely from the configurational entropy contribution. A modified hard-sphere model including the deformability of spheres in addition to the change in configurational entropy is developed. This model naturally explains the observation that the Grüneisen parameter decreases with increasing pressure for solids but increases for liquids. |
Refinement of the structure of siderite up to 54 GPa |
| Barbara Lavina HiPSEC-University of Nevada Las Vegas lavina@physics.unlv.edu Przemyslaw Dera, GSECARS, The University of Chicago Robert T. Downs, University of Arizona, Tucson, USA Oliver Tschauner Wenge Yang, HPCAT, Carnegie Institution of Washington, Argonne, USA Guoyin Shen, HPCAT, Carnegie Institution of Washington, Argonne, USA Malcom Nicol |
| Facility: APS-HPCAT Format: Poster |
| Robust structural refinements from single crystal diffraction data of siderite, FeCO3, will be presented. Refinements has been conducted in the range 0-54 GPa, with unvaried quality over the entire range. Results offer a very detailed description of the effects of the spin transition on the structure geometry. Data were collected in the omega scan mode at the Station 16BMD, APS, ANL. About 40 independent reflections were extracted from the pattern and constrained very reliably 4 parameters: the scale factor, the oxygen positional parameter and the isotropic displacement parameters of Fe an O. The general compression mechanism of the rhombohedral carbonates, with a large axial anisotropy, a rigid CO3 unit, and a octahedron experiencing the largest deformations is confirmed in siderite also after the spin transition. However, fine variations in the distortion and bond distances trends can be distinguished, allowing evaluation subtle changing in the bonding of siderite as effect of the spin transition. Support from DOE, NSF and NNSA are gratefully acknowledged. |
Recent Development on Measurement of Anelasticity of Minerals at High Pressures |
| Li Li Stony Brook University lilli@ic.sunysb.edu Liping Wang, Michael Vaughan, Donald J. Weidner |
| Facility: NSLS-X17B2 (MAC) Format: Poster |
| Time-resolved stress-strain measurements allow us to explore dynamic behaviors spanning anelastic effects (at small strain) to transient creep (at large strains). Anelasticity defines the frequency dependence of acoustic velocities. It bridges the sound velocities measured at high frequencies (MHz-GHz) to seismic waves (mHz). There is a lack of knowledge of anelasticity at mantle P-T. In particular, phase transitions can have strong effects on sound velocities and attenuation. This poster present the recent results on anelasticity of minerals measured at mantle P-T. We find that (1) both frequency and temperature have large effect on Young?s modulus and attenuation of the klb-1 sample. Silicate melts do not appreciably affect the Young?s modulus, grain boundary interactions dominate the change of Young?s modulus and Q-1. (2) ferroelastic phase transition affects the attenuation behavior of perovskite (neighborite) at high P. Large attenuation occurs in the orthorhombic phase which is believed to be due to the domain motion. |
Phase transition studies for amorphous and crystalline materials under high pressure conditions using synchrotron x-ray imaging and diffraction tomographic techniques |
| Haozhe Liu Harbin Institute of Technology haozhe@hit.edu.cn Haozhe Liu1, Luhong Wang1, Xianghui Xiao2, Peter Lee2, Jon Almer2, Francesco De Carlo2, Wenge Yang3, Russell Hemley4, Ho-kwang Mao4 1. Natural Science Research Center, Harbin Institute of Technology, Harbin 150080, China 2. Advanced Photon Source, Argonne National Laboratory, Argonne, IL, 60439 3. HPCAT, Carnegie Institution of Washington, Advanced Photon Source, Argonne, IL, 60439 4. Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015 |
| Facility: APS-HPCAT Format: Poster |
| The novel developed synchrotron x-ray imaging and diffraction tomographic methods combined with high pressure diamond anvil cell technique offer great opportunity for the research on structural stability of materials upon compression. The study of polymorphism and polyamorphism in pressure domain will undoubtedly broaden our horizons and perspectives of the states of matter in general, and may have a significant impact on the existing theories about the structure, formation, and evolution of crystal and amorphous materials. Metallic glasses were selected to test the pressure induced polyamorphism. The procedure of the pressure-induced amorphous state selenium to crystalline state under pressure is another subject in this project. The structural evolution of powder and amorphous materials under pressure, as well as the time dependence of the crystallization procedure were studied by x-ray diffraction and imaging tomography methods in 3-D space domain. These will provide new insight on the nature of phase transition, provide new invitation for the electronic theoretical studies for the phase stability, and improve our understanding of the kinetic process of the common pressure induced crystallization and phase transitions. |
SEM and EBSD Study on the Microstructure of Deformed Olivine at High Pressure and Low Temperature |
| Hongbo Long Stony Brook University hlong@ic.sunysb.edu Donald J Weidner |
| Facility: NSLS-X17B2 (MAC) Format: Poster |
| SEM and EBSD studies have been done for the recovered olivine specimens from the deformation experiments performed at subduction zone conditions and mantle pressure, on a D-DIA apparatus, SAM85, at X17B2 of NSLS. The SEM results show that compression and deformation make the grain size of olivine into sub-micron level. The pseudo grains in the recovered sample may be the relics developed from the starting olivine grains and become foliations vertical to the deforming axis undergoing the deformation. In the EBSD study, The LPO shows that the predominant active slip systems of olivine at subduction zone condition and mantle pressure evolve from {hk0}[001] (h > k) and {110}[001] at 500¡ãC to {hk0}[001] (h > k) and (100)[001] at 700¡ãC. The occurrence of active (100)[001] represents that power-law creep has involved in playing an important role together with the low temperature plasticity. Predominant active (100)[001] system of olivine in the slab may result in the seismic anisotropy different from the conventional mantle. |
Complex anisotropy in D" beneath the eastern Pacific from SKS-SKKS splitting discrepancies |
| Maureen D. Long Yale University maureen.long@yale.edu |
| Facility: None Format: Poster |
| Although observations of seismic anisotropy in the lowermost mantle are abundant, the mechanism which generates anisotropy in the D" layer is not well understood. Most observational constraints on D" anisotropy come from the splitting of shear waves that propagate (nearly) horizontally through the lowermost mantle. However, anisotropy in the D" layer can also give rise to discrepancies in shear wave splitting for SKS and SKKS phases for the same event-station pair, as these phases sample different regions of the lowermost mantle. Here I report observations of strongly discrepant SKS-SKKS splitting observed at broadband stations in western Mexico and California. In particular, strong SKKS splitting with fast polarization directions near ~ 60º and delay times up to ~ 3 s is observed for a group of raypaths that sample a region of the D" layer beneath the eastern Pacific Ocean. A comparison of SKKS splitting with SKS splitting observed from the same events, as well as with SKS splitting observed at a variety of backazimuths at each station, suggests that the anomalous anisotropic structure is in the lowermost mantle. My preferred model for the unusual anisotropic geometry in this region is large shear deformation in D" at the edge of a region where slab material impinges upon the core-mantle boundary, resulting in lattice preferred orientation of lower mantle minerals. |
Teaching Mineral Physics across the Geoscience Curriculum |
| David W Mogk Department of Earth Sciences, Montana State University mogk@montana.edu |
| Facility: None Format: Poster |
| A new instructional website, Teaching Mineral Physics across the Geoscience Curriculum, is being developed as a collaborative project between COMPRES and the On the Cutting Edge program for geoscience faculty development. Using modern information technologies, we are currently discovering, aggregating, organizing, reviewing, and disseminating a wide range of instructional resources related to mineral physics including course notes, tutorials, demonstrations, PowerPoint presentations, laboratory exercises, and teaching activities (e.g. problem sets). The intent of this webpage is to facilitate inclusion of exciting new research methods and results into instructional activities and into the geoscience curriculum, and to help mineral physics researchers address NSF's "critierion two" requirement of demonstrating broader impacts. To review the current collections of resources, and to contribute new materials, please visit: http://serc.carleton.edu/NAGTWorkshops/mineralogy/mineral_physics.html. |
Towards Mbar-pressures at deep Earth’s interior representing samples - the challenge of new light source based high pressure techniques for process research of the next decade and beyond |
| Hans J. Mueller GFZ German Research Centre for Geosciences hjmuel@gfz-potsdam.de Christian Lathe |
| Facility: Other Format: Poster |
| The Earth’s mantle has a mass of about 4.08 . 10exp21 tons and represents 68 % of the total mass of the Earth. The Earth’s mantle is only accessible by indirect methods, first of all seismological studies. The interpretation of these seismic data from the Earth’s deep interior requires measurements of the elastic and inelastic properties of Earth materials under experimental simulated mantle and core-mantle boundary (CMB) conditions, i.e. conditions representative for Earth’s deep interior. New seismological techniques based on the dense global station network resulted in fundamental improved knowledge about deep structures, as subduction down to the CMB, accumulation of low viscous material above the CMB, detection of rising plumes etc. One fundamental lesson from that is - contrary to classical imaginations deep Earth is just the opposite of beeing simple and stratified. There are clear relations between the Earth’s interior and surface and atmospheric processes as climat development. The investigation of complex processes requires, technically speaking, strong controlling of gradients and assuring of minimum dimensions to truly represent natural conditions. There is also a strong indication of widespread unquenchable phases at extreme conditions requiring necessarily in situ observations. Recent geophysics sets of the tasks, recent material sciences and engineering delivers the tools, recent light source based mineral physics supplies recent numeric modeling with indispensable data to solve the geodynamic problems. The paper presents and summarizes some innovative high pressure techniques developed or under development for geoscientific experiments at light sources worldwide, including the techniques and results of the corresponding author’s experiments at DESY beamlines. |
First-Principles Calculation of Density Dependence of Lattice Anharmonicity in NaCl (Sodium Chloride) |
| Moses C Ntam Auburn University, Auburn Alabama ntammos@auburn.edu Jianjun Dong Auburn University Auburn Alabama |
| Facility: None Format: Poster |
| Lattice thermal conductivity remains one of the least constrained properties of minerals, especially at high pressures. NaCl is one of few materials whose lattice thermal conductivity has been measured using diverse experimental techniques, thus serves as a very good test system for the theoretical study of the pressure effects on thermal conductivity. As the first step, we performed a series of first principle calculations of harmonic and anharmonic lattice dynamics in NaCl at various densities. Using a real-space super-cell technique, we directly calculated the irreducible sets of elements of the 2nd order force constant matrices and the 3rd order anharmonicity tensors. The complete force constant matrices and anharmonicity tensors are then reconstructed based on the group theoretical analysis. The dependence of anharmonicity tensors on density is then discussed in this poster. The outcome of this study will be adopted to directly estimate phonon scattering rates for thermal conductivity calculations. |
Viscosity of Komatiite Liquids at High Pressures |
| Lara O'Dwyer Brown Department of Geology, University of California at Davis lodwyer@ucdavis.edu Charles E. Lesher Hidenori Terasaki (Department of Earth and Planetary Materials Science, Tohoku University) |
| Facility: Other Format: Poster |
| The viscosities of komatiite liquids at high pressures and temperatures were investigated using the in-situ falling sphere technique at BL04B1, SPring-8. Komatiites are naturally occurring magmas, rich in network modifiers. They are derived from the early Earth?s mantle and found in the rock record. Despite the refractory and fluid nature of komatiite, we successfully measured the viscosity of molten komatiites from Gorgona Island, Colombia (MgO = 17.8 wt.%) between 11 and 13 GPa at 2000 C, and from Belingwe, Zimbabwe (MgO = 28.14 wt.%) from 12 to 14 GPa at 2000 C. Under isothermal conditions, the viscosity of Gorgona Island komatiite melt increased with pressure, consistent with our previous measurements at lower pressures for this composition. We interpreted this positive pressure dependence as the result of reductions in interatomic space diminishing the free volume of the liquid as it was compressed. The viscosity of molten komatiite from Belingwe also increased up to 12 GPa, however between 12 and 14 GPa the viscosity did not change. In previous studies of network modifier-rich silicate melt viscosity, authors have found reversals in the pressure dependence [1] [2]. While we detected a change in the pressure dependence of the Belingwe liquid viscosity, we cannot confirm a viscosity maximum without data at higher pressure. It is clear, however, that structural changes other than reductions in the liquid?s free volume are influencing the viscosity in these depolymerized compositions. [1] Reid J.E., Suzuki A., FunakoshiK-I., Terasaki H., Poe B.T., Rubie D.C. and Ohtani E. (2003) The viscosity of CaMgSi2O6 liquid at pressures up to 13 GPa. [2] Liebske C., Schmickler B., Terasaki H., Poe B. T., Suzuki A., Funakoshi K., Ando R., and Rubie D. C. (2006) Viscosity of peridotite liquid up to 13 GPa: Implications for magma ocean viscosities. Earth and Planetary Science Letters 240, 589 - 604. |
Tetrahedral Occupancy of Ferric Iron in (Mg,Fe)O: implications for point defects in the lower mantle. |
| Kazuhiko Otsuka Yale University kazuhiko.otsuka@yale.edu Catherine McCammon (Bayerisches Geoinstitut) Shun-ichiro Karato |
| Facility: Other Format: Poster |
| (Mg,Fe)O, the second most abundant phase in the lower mantle, plays important roles in the transport properties (atomic diffusivity, viscosity and electrical conductivity) of the deep Earth. One of the unique features of (Mg,Fe)O is the solubility competition between positively-charged defects of Fe3+ and H+, which will influence the way in which transport properties depend on oxidation and hydration states of the Earth. The concentration of both Fe3+ and H+ changes with pressure, temperature and other chemical parameters. Therefore, it is important to understand dissolution mechanisms of Fe3+ and H in (Mg,Fe)O as a function of these parameters. In this study, we have conducted Mössbauer spectroscopy of (Mg0.8Fe0.2)O single crystals synthesized at temperatures from 1400 to 2000 °C and pressures from 5 to 15 GPa with Re-ReO2 and Mo-MoO2 oxygen fugacity buffers to constrain Fe3+ concentration and site-occupation in the lower mantle. The observed isomer shift of Mössbauer spectra suggest that Fe3+ occupies two crystallographic positions in (Mg,Fe)O: octahedrally- and tetrahedrally-coordinated cation sites. The relative occupancy between two sites varies with Fe3+ concentration such that tetrahedral Fe3+ dominates over octahedral Fe3+ at low Fe3+ concentration. We formulated a thermodynamic model of point defect dissolution in (Mg,Fe)O, which demonstrates that the concentration of Fe3+ in tetrahedral occupancy is less sensitive to pressure and oxygen fugacity than Fe3+ in octahedral occupancy due to the effect of configurational entropy. Our results suggest that (Mg,Fe)O accommodates Fe3+ mostly in the tetrahedral site in the lower mantle. The concentration of Fe3+ at the top of the lower mantle is in between two values of hydrogen solubility in (Mg,Fe)O reported by Bolfan Casanova et al (2002) and Murakami et al (2002). The conditions of solubility crossover between Fe3+ and H+ are not resolved due to the large uncertainty of hydrogen solubility. The influence of H+ in the lower mantle may be marked depending on the conditions of solubility crossover between H+ and Fe3+. |
Melting Behavior and Chemical Properties of the Iron-Carbon System |
| Vitali Prakapenka University of Chicago prakapenka@cars.uchicago.edu I. Kantor, A. Kantor, P. Dera, M.L. Rivers and S.R. Sutton |
| Facility: APS-GSECARS Format: Poster |
| One of the most challenging experiments related to the laser heating technique in the diamond anvil cell (DAC) is an unambiguous x-ray based detection of melting by recording high quality diffuse x-ray scattering from molten materials at high pressure. Employing a newly developed, advanced, flat top laser heating system at GSECARS, we were able to perform on-line melting experiments at pressures up to 60 GPa. The capability to maintain the molten sample in the DAC for a relatively long time (at least 60 s) allowed us to collect high quality x-ray scattering data suitable for structure analysis even from low-Z molten materials, such as Si, Ge, Fe, Fe3C, Fe7C3 etc. In this work, we focused on the melting behavior and chemical properties of the iron-carbon system at pressures up to ~170 GPa studied with on-line micro x-ray diffraction in a double sided laser heated DAC at GSECARS (Sector 13, APS). Iron carbides (Fe3$, Fe7C3) were synthesized it in-situ in the DAC from various mixtures of Fe and C powders with different atomic ratios. We have found that the chemical reaction between iron and carbon takes place independent of the structure of starting phases of iron fcc or hcp and carbon (graphite or diamond). The reaction temperature increased gradually from ~1000 K to ~1700 K as pressure increased from 6 GPa to 155 GPa. The melting temperature of iron carbide was found to be systematically lower than for iron by ~300-400 degrees in the pressure range 20-60 GPa. The experimentally measured structure factor and related pair distribution function of iron carbide melt were analyzed and compared with pure iron data at related pressures. High-pressure, high-temperature stability of iron carbide phases at the relevant Earth's mantle-core conditions and physical/chemical properties of iron-carbon melts provide important constraints on models of the formation of D" layer and interactions at the core mantle boundary. Implications of these results for the composition and structure of the Earth's interior will be discussed. |
Raman Spectroscopy Study of Carbon Nanotube at High Pressures |
| Srinija Repalle Florida international university srepa001@fiu.edu Jiuhua Chen, Vadym Drodz |
| Facility: Other Format: Poster |
| We studied the aligned multi-wall carbon nanotubes (MWCNTs) for their structural and bonding changes under high pressure using Raman Spectroscopy. The sample was treated under the combinations of high pressure (2-20GPa) and high temperature (RT-5000C). Comparison of data before and after the high pressure and high temperature treatments indicates that intertube bonding may be introduced during the high pressure and high temperature treatment. Details about the experiments and the data analysis will be reported. The Raman data provides a potential source of information regarding bonding changes to determine the pressure and temperature induced change in carbon nanotubes. |
areaDetector: Software for 2-D detectors in EPICS |
| Mark Rivers University of Chicago, Center for Advanced Radiation Sources rivers@cars.uchicago.edu |
| Facility: APS-GSECARS Format: Poster |
| Nearly all high-pressure synchrotron beamlines use 2-D detectors, including visible light CCD cameras for imaging, CCD detectors for optical spectroscopy, and x-ray detection using online image plates, CCDs, pixel array detectors and amorphous silicon flat panel detectors. In most cases these detectors need to be controlled from the beamline control system, and it can be very useful to have the detector data immediately available to the control system for display and analysis. Most COMPRES beamlines use the EPICS control system for experimental control and data acquisition. EPICS is an open-source, distributed, client-server control system toolkit that provides great flexibilty and support for a large number of devices used on beamlines. areaDetector is a new EPICS module designed to support 2-D detectors. It is modular C++ code that greatly simplifies the task of writing a support for a new detector. It also supports the concept of plugins, which are software modules that receive detector data from the driver and process it in some way. Existing plugins perform Region-Of-Interest extraction and analysis, file saving (in netCDF, TIFF and JPEG formats), color conversion, and export to EPICS records for image display in clients like ImageJ and IDL. Drivers have now been written for most detectors in use on COMPRES beamlines, including: - marCCD (Rayonix) CCD detector - mar345 online imaging plate - Firewire (IEEE 1394 DCAM) cameras - Prosilica Gigabit Ethernet cameras - Pilatus pixel-array detector - Princeton Instruments and Photometrics CCD cameras (using WinView and WinSpec programs) - Perkin-Elmer amorphous silicon flat-panel detectors By using a consistent framework, a common set of control variables (EPICS PVs), a single display viewer and single set of analysis plugins can be used with any of these detectors. |
Does Volume Change Drive the Charge Disproportionation of Iron in the Lower Mantle? |
| Sang-Heon Shim Massachusetts Institute of Technology sangshim@MIT.EDU Krystle Catalli |
| Facility: APS-GSECARS Format: Poster |
| The charge disproportionation of iron, 3Fe2+ (silicate) -> 2Fe2+(silicate) + Fe(metal), have been proposed to explain the high concentration of Fe in mantle silicates synthesized at high pressure . The disproportionation is hypothesized to be driven by the smaller volume of the Fe3+ + Fe assemblage than the Fe2+ assemblage at the lower mantle. We have measured effects of the Fe valence state on the volumes of mantle perovskite (Pv) and post-perovskite (PPv). For Al-free Pv, Fe3+ expands the volume more than Fe2+ throughout the lower mantle. In an Al-free pyrolitic system, volumes of both Fe3+ + Fe and Fe2+ assemblages become similar to each other at the shallower lower mantle due to the participation of ferropericlase but volume disfavors the Fe3+ + Fe assemblage at the lowermost mantle. For Al-bearing system, the volume collapse of Pv by the Al--Fe site mixing and the Fe3+ spin transition would make volume of the Fe3+ + Fe assemblage smaller at the lowermost mantle. At the D" region where the PPv phase is stable, the Fe3+ + Fe assemblage has smaller volume in both Al-free and Al-bearing systems. These results suggest that crystal chemistry may be an important factor to consider for the valence state of Fe in the lower mantle and the concentration of Fe3+ in silicates could vary with depth due to effects from the Fe spin transition and the PPv transition at different pressures. |
Synchrotron X-ray Diffraction Studies of Metal-Oxide Pairs |
| Gregory A Shofner University of Maryland, Department of Geology gshofner@umd.edu Andrew Campbell, University of Maryland, Department of Geology Lisa Danielson and Kevin Righter, NASA, Johnson Space Center |
| Facility: NSLS-X17C (DAC) Format: Poster |
| Oxygen fugacity (fO2) controls multivalent phase equilibria and partitioning of redox-sensitive elements, and it is important to understand this thermodynamic parameter in experimental runs as well as natural systems. Constructing fO2 buffers to pressures and temperatures corresponding to the Earth's deep interior requires precise determinations of the difference in volume (∆V) between the buffer phases over a range of P-T conditions. Synchrotron x-ray diffraction data was collected for the present studies to measure unit-cell volumes of metals and their oxides (Co-CoO, Cr-Cr2O3, Mo-MoO2, W-WO2) under varied pressure and temperature conditions, to construct high pressure fO2 buffer curves for these systems. Experiments were conducted in diamond anvil cells (DAC) at NSLS beamline X17C, and in the multi anvil press (MAP) at APS beamline 13-ID-GSECARS. The DAC experiments were at room temperature and reached pressures up to 75 GPa. The MAP experiments (Co-CoO and Cr-Cr2O3 only) were at temperatures up to 1600˚C and at pressures up to 20 GPa. For each experiment, both the metal and its oxide were present, thus the unit-cell volume measurements were made for both phases under the same experimental conditions, minimizing the uncertainty in calculating the ΔV between the phases. Bulk moduli (K0) and their derivatives (Ko?) were determined for each phase. Room temperature values of K0 and K0? for Co, Cr, Mo, W, and Cr2O3 were within experimental uncertainty of published data for these phases. K0 and Ko? for MoO2 (K0=209, K0?=3.7) and WO2 (K0=302, K0?=4) have not been previously reported. Both MoO2 and WO2 were determined to be monoclinic up to approximately 35 GPa, but appeared to transform to an unidentified crystal structure at higher pressures. The reversible structural transformation, from the HCP to FCC, was observed in Co at temperatures above approximately 700˚C. Using the experimentally constrained equations of state, fO2 buffer curves were calculated for the Co-CoO and Cr-Cr2O3 (CRO) systems. The Co-CoO buffer ranges from approximately +4 to +2 log units above the IW buffer, whereas the CRO buffer ranges from approximately -9 to -3 log units below the IW buffer, over a temperature range of 700 to 1900˚C. |
Novel Large Volume Multianvil Cells: New experimental possibilities for Earth Science and Solid State Chemistry |
| Emil Stoyanov Arizona State University emil.stoyanov@asu.edu Kati Puhakainen (Arizona State Universiy) Kurt Leinenweber (Arizona State University) Ulrich Häussermann (Arizona State University) |
| Facility: Other Format: Poster |
| We present two large volume multianvil cells with an octahedral edge length of 18mm and 25mm. Both cells are especially designed to accommodate large samples with minimal thermal gradients. The sample sizes in the 18/12 and 25/15 assemblies are up to 135mm3 and 330mm3, respectively. The measured thermal gradients at 1200°C vary between 5-10°C/mm (18/12) and 15-20°C/mm (25/15). The pressure calibrations of the two cells were done at room temperature and 1200°C. It is noticeable, that using a conventional Walker-type press one can easily produce up to 0.5g of high pressure phase (eg. coesite) using the newly designed 25/15 cell. These large volume cells are especially useful for high-pressure materials synthesis where large sample quantities are desirable for comprehensive structure and property characterization of products. As a particular example we show the synthesis of Li2PtH6 from LiH, Pt, and hydrogen generated by the thermal decomposition of an internal source. Li2PtH6 (space group Fm-3m, a = 6.758(2) Å) contains Pt in the oxidation state IV and is only accessible at pressures higher than 6 GPa. The synthesis of Li2PtH6 shows the potential of gigapascal hydrogenations to afford new hydrogen dominant materials, which can be recovered and subsequently investigated at ambient pressure. An important prerequisite for the synthesis of new H-dominant materials by multi anvil techniques are stable large volume assemblies that can accommodate the H-source and still yield an appreciable quantity of reaction product. |
A Journey Toward the Center of the Earth - Iron/Light-Element Alloys at Extreme Conditions and Their Implications for the Earth's Core |
| Matthew L Whitaker Department of Geosciences, Stony Brook University, Stony Brook, NY 11794-2100 matt@mattwhitaker.net Wei Liu, Liping Wang, Baosheng Li Mineral Physics Institute, Stony Brook University, Stony Brook, NY 11794-2100 |
| Facility: NSLS-X17B2 (MAC) Format: Poster |
| In order to determine what elements may possibly be constituents of the inner core, and in what abundances, experiments were conducted to determine the behavior and physical properties of iron minerals under extreme conditions of pressure and temperature. Static compression studies were conducted at room temperature on 4 materials using synchrotron X-ray diffraction in Diamond Anvil Cells: Fe3P to 14 GPa, FeS2 to 13.2 GPa, FeS to 11.6 GPa, and epsilon-FeSi to 15.1 GPa. Ultrasonic interferometry was used in combination with synchrotron X-radiation in a multi-anvil apparatus at ambient temperatures to determine the compressional and shear wave velocities and unit-cell volumes of FeS2 to 9.6 GPa, FeS to 10.4 GPa, and epsilon-FeSi to 12 GPa. These last two materials were also studied using ultrasonics at high temperature and pressure, up to 8.3 GPa and 1073 K for FeS, and to 8 GPa and 1273 K for epsilon-FeSi. The results of these experiments and their implications and preliminary conclusions will be presented. |
Compatibility of K and Rb with Fe at High Pressure and Implications for the Deep Earth |
| Sabrina ARA Whitaker The Ohio State University huggins.43@osu.edu 1Whitaker, S, 1Reaman, D M, 1Kabbes, J E, 1 Piggott, J S, 2Hovis, G L, 3Campbell, A J, 4Cottrell, E, 5Henry P. Scott,1Panero, W R 1The Ohio State University, School of Earth Sciences 125 S. Oval Dr 275 Mendenhall Laboratory, Columbus, OH 43210, United States , 2Lafayette College, Department of Geology and Environmental Geosciences , Lafayette College, Easton, PA 18042, United States, hovisguy@lafayette.edu ,3University of Maryland, Department of Geology University of Maryland, College Park, MD 20742-4211, United States, ajc@umd.edu, 4Smithsonian Institute, Department of Mineral Sciences Smithsonian Institute Washington, DC 20013, United States, cottrelle@si.edu, 5 Indiana University, South Bend , Department of Physics and Astronomy, Indiana, USA, hpscott@iusb.edu |
| Facility: NSLS-X17C (DAC) Format: Poster |
| Long-lived radionuclides such as potassium, uranium, and thorium are sources of heat generation in the interior of the Earth. 40K decays to 40Ca and 40Ar with a half-life of about 1.25 Gy, responsible for ~ 10% of the Earth?s current heat production. While not a major component of heat production, 87Rb decays to 87Sr with a half-life of 48 Gy, and the 87Sr/86Sr ratio is taken as a tracer for geochemical reservoirs throughout Earth history. Previous experiments on potassium solubility in iron at high pressures show varying results as to the possible concentration of potassium in the core. While there have not been any previous studies on rubidium, it often substitutes for potassium in minerals due to its similar ionic charge and radius and therefore similar results are expected. This study evaluates the effect of sample preparation on the effect of solubility of Rb or K in iron. All samples after quench showed ~ 2% expansion of the iron lattice when analyzed by X-ray diffraction, for a distribution coefficient of 0.033 at 2500 K. Samples loaded with powder in air varied more than those loaded in a nitrogen environment or with foil. Complimentary TEM and nano ? SEM studies found the amount of Rb alloyed with iron to be below the detection limit (3000 ppm), placing an upper bound on the distribution coefficient of 0.012, broadly consistent with the results from XRD. Therefore, the upper bound for K and Rb in the core is inferred to be 8 ppm and 17 ppb, respectively. This implies an upper bound of 5 X 1010 W for the power in the core due to radioactive decay of K. The possibility of Rb in the core could impact the cycling and distribution of Rb with respect to Sr, affecting the interpretation of Sr87/Sr86 with respect to mantle geochemical processes. |
First-principles study of structural instability and thermal properties of silicon nitride under high pressure |
| Bin Xu Physics Department, Auburn University, AL xubin01@auburn.edu Jianjun Dong |
| Facility: None Format: Poster |
| beta-Si3N4 is observed to transit into the cubic spinel gamma phase at high pressure, while laser heating is found necessary. At room temperature, Zerr observed a new delta phase obtained on compression of beta phase above 34 GPa [Zerr, 2001], whereas the structure was not fully determined. A recent experiment from McMillan et al reproduced Zerr?s findings on delta-Si3N4, but excluded the willemite-II cubic structure [McMillan et al, 2007]. We have theoretically investigated the metastability of beta-Si3N4 under high pressure. The equilibrium beta-to-delta transition pressure as a function of temperature has been calculated and compared with previous experimental and theoretical works. In case the beta-to-deltatransition is bypassed, we predict a first-order transition from beta phase to a ?post-phenacite? phase with P3 symmetry at about Pt = 38.5 GPa. This transition is driven by the instability due to soft phonon modes at Gamma-point. The small beta-to-P3 activation barrier (~67 meV/atom) obtained from the 2D potential-energy surface (PES) at Pt is consistent with the occurrence of this transition at room temperature. In addition, the thermal expansion coefficients (TEC) of alpha, beta and gamma-Si3N4 are calculated. The negative TEC in alpha and beta-Si3N4 at low temperature is ascribed to some low-frequency phonon modes with negative Grüneisen ratios. |
First-principles study of the mechanism for B4-to-B1 phase transformation in AlN |
| Bin Xu Physics Department, Auburn University, AL xubin01@auburn.edu Jianjun Dong (Physics Department, Auburn University); Harold Stokes and Dorian Hatch (Department of Physics and Astronomy, Brigham Young University) |
| Facility: None Format: Poster |
| We present a recent ab initio calculation of activation barriers for the B4-to-B1 transition in AlN based on five transition paths (TPs) proposed by Stokes et al [Stokes et al, 2005]. These TPs are bond preserving and were explained by a common bilayer sliding mechanism. Our calculation shows that all five TPs give comparable magnitudes of activation barriers delta_H at pressures from 0 GPa to 30 GPa. We reinterpret the bilayer sliding mechanism with the long-range transformation pattern composed of four-atom "transition units" [Cai et al, 2007] (two different orientations). The transformation of "transition unit" is equivalent to the path along TP1 (with Cmc2₁ symmetry). Comparable delta_H from different TPs leads to the conclusion that the energetics of the B4-to-B1 transformation is determined by the "transition unit", whereas the long-range pattern is less important. Furthermore, the difference in strains of different TPs is not a major factor for at least the wurtzite-to-rocksalt transition in AlN. Our estimated forward and backward barrier heights are consistent with experimental observation and previous calculations. At 9.85 GPa (the predicted equilibrium transition pressure) the B4-to-B1 activation enthalpy barrier delta_H is about 0.13 eV/atom, anddelta_H decreases with pressure. |
Transformation path study for the corundum-to-Rh2O3(II) transition in Al2O3 |
| Bin Xu Physics Department, Auburn University, AL xubin01@auburn.edu Jianjun Dong (Physics Department, Auburn University); Harold Stokes and Dorian Hatch (Department of Physics and Astronomy, Brigham Young University) |
| Facility: None Format: Poster |
| Alumina (Al2O3) has attracted much attention in high-pressure technology and geophysics. X-ray diffraction experiment shows that corundum phase Al2O3 can stably exist up to 175 GPa. However, with laser heating, corundum phase is found to transform into the Rh2O3(II) structure at about 90 GPa. The meta-stability between 90 to 175 GPa at lower temperature indicates the existence of a large kinetic barrier along the transition pathway from corundum to Rh2O3(II) phase. In this study, we show that the rhombohedral corundum phase can also be interpreted as a slightly distorted orthorhombic structure with monoclinic symmetry, which is closely related to the Rh₂O₃(II) phase. We proposed a microscopic transformation mechanism for the corundum-to-Rh₂O₃(II) transition, which is characterized by one bond breaking-and-reforming (OB-BAR) for 1/3 of the four-coordinated O atoms (4g site) and half of the six-coordinated Al atoms (4g site). Based on the calculated backward (Rh₂O₃(II)-to-corundum) enthalpy barrier height, we predict that the high-pressure Rh₂O₃(II) phase is unlikely to be quenchable to the ambient conditions. In addition, the elastic properties of corundum and Rh₂O₃(II) phase are found to be very comparable. |
Inelastic X-ray Scattering Capabilities at the Advanced Photon Source |
| Hasan Yavas Department of Geology, University of Illinois yavas@aps.anl.gov Wolfgang Sturhahn, Advanced Photon Source, Argonne National Laboratory Jay D. Bass, Department of Geology, University of Illinois Jennifer M. Jackson, Seismological Laboratory, Division of Geological and Planetary Sciences, California Institute of Technology |
| Facility: Other Format: Poster |
| The inelastic X-ray scattering (IXS) techniques at 3-ID and 30-ID beamlines of Advanced Photon Source can be categorized into three broad areas: 1) Momentum-resolved Inelastic X-ray Scattering directly gives the dispersion relation of low-energy collective excitations like phonons. Such measurements provide directional information on vibrational and elastic properties, such as the elastic tensor and sound velocities. 2) Synchrotron Moessbauer Spectroscopy (SMS) provides information on magnetic properties and valence state of iron in minerals and high-pressure phases. It is also sensitive to solid-melt transitions. 3) Nuclear Resonant Inelastic X-ray Scattering (NRIXS) provides information on vibrational and elastic properties, such as the phonon density of states and sound velocities. All three techniques can now be performed using small samples in a diamond anvil cell (DAC) with the new focusing capability added to the momentum resolved IXS station of 3-ID. With this new addition, 3-ID offers higher-flux with comperable resolution alternative to 30-ID. It is desirable to characterize materials by IXS techniques while they are at high pressure and high temperature conditions, similar to those in the deep Earth. For this purpose a laser heating system was installed for SMS and NRIXS at sector 3-ID at the Advanced Photon Source. At the moment external heating method is employed for momentum-resolved measurements. Examples of the respective IXS experiments that have been performed at the 3-ID and 30-ID beamlines will be shared. Additionally, the developments and planned improvements that are relevant to Earth and planetary sciences will be presented. This work is supported by COMPRES under NSF Cooperative Agreement EAR 06-49658. Work at Argonne National Laboratory was supported by the U.S. DOE, Office of Basic Energy Sciences, under contract No. DE-AC02-06CH11357. |
Pressure response of iron?s hyperfine parameters in (Mg_{0.87}Fe_{0.13})SiO_3 orthopyroxene at room temperature |
| Dongzhou Zhang Seismological Laboratory, Division of Geological and Planetary Sciences, California Institute of Tec dzzhang@caltech.edu Jennifer M. Jackson(Seismological Laboratory, Division of Geological and Planetary Sciences, California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125, USA)and Wolfgang Sturhahn(Advanced Photon Source, Argonne National Laboratory, 9700 S. Cass Ave., Argonne, IL 60439, USA) |
| Facility: Other Format: Poster |
| Iron-bearing orthopyroxene (Opx) is an abundant mineral in the Earth?s crust and upper mantle. Understanding its structural response to relevant mantle conditions will provide important information for seismological and dynamical modeling of this region. Although X-ray diffraction studies have been carried out at high pressure on iron-bearing Opx, details on the specific site behavior of iron in the complex Opx crystal structure are less understood at relevant mantle conditions. Mössbauer spectroscopy allows one to uniquely probe the site-specific behavior of iron in solid materials by direct determination of iron?s hyperfine fields, namely its quadrupole splitting and isomer shift. Therefore, it is especially suitable for the exploration of iron?s site-specific behaviors in Opx. We loaded a synthetic 57Fe-enriched (Mg_{0.87}Fe_{0.13})SiO_3 powdered Opx sample into a diamond anvil cell using NaCl as a pressure-transmitting medium. Synchrotron Mössbauer Spectroscopy (SMS) was carried out at Sector 3-ID of the Advanced Photon Source at Argonne National Laboratory. The data were collected up to 36 GPa using stainless steel as a reference absorber to accurately constrain the isomer shifts of the M1 and M2 sites in Opx. The SMS spectra were analyzed with the CONUSS software package. The hyperfine parameters of the M1 and M2 sites at room pressure are in excellent agreement with previous literature values obtained using conventional Mössbauer spectroscopy. We find that the quadrupole splitting of M1 and M2 sites increases with pressure up to 10 GPa. At pressure beyond ~15 GPa, analysis of the spectra indicates that a small portion of the Opx is in the amorphous state. The pressure response of the equilibrium intracrystalline distribution coefficient (K_D) will also be presented. |