Bulletin of the American Physical Society
18th Biennial Intl. Conference of the APS Topical Group on Shock Compression of Condensed Matter held in conjunction with the 24th Biennial Intl. Conference of the Intl. Association for the Advancement of High Pressure Science and Technology (AIRAPT)
Volume 58, Number 7
Sunday–Friday, July 7–12, 2013; Seattle, Washington
Session O5: GP1: Geophysics IV |
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Chair: Michael Brown, University of Washington Room: Cascade I |
Wednesday, July 10, 2013 9:15AM - 9:30AM |
O5.00001: EXAFS study of solid iron up to 560 GPa Yuan Ping, F. Coppari, D. Hicks, B. Yaakobi, D. Fratanduono, S. Hamel, J. Eggert, J. Rygg, R. Smith, D. Swift, T. Boehly, G. Collins Dynamic compression by multiple shocks is used to compress iron up to 560 GPa (5.6 Mbar), the highest solid-state pressure yet attained for iron in the laboratory. EXAFS (extended x-ray absorption fine structure) spectroscopy offers simultaneous density, temperature and local-structure measurements for compressed iron, providing highest-pressure data up to date for constraining solid state theory and evolution models for many newly discovered extra-solar terrestrial planets. The data show that the close-packed structure of iron is stable up to 560 GPa, the temperature at peak compression is significantly higher than expected from pure compressive work, and the strength of iron many times greater than expected from lower pressure data. [Preview Abstract] |
Wednesday, July 10, 2013 9:30AM - 9:45AM |
O5.00002: Single crystal crystallography of geomaterials at 100 GPa and above Leonid Dubrovinsky, Natalia Dubrovinskaia, Elena Bykova, Konstantin Glazyrin, Tiziana Boffa Ballaran, Catherene McCammon, Anastasia Kantor, Marco Merlini, Michael Hanfland, Alexander Chumakov Modern science and technology rely on the fundamental knowledge of matter that is provided by crystallographic studies. The most reliable information about crystal structures and their response to changes in pressure and temperature is obtained from single crystal diffraction experiments. Advances in diamond anvil cell techniques (DACs) and modern X-ray sources have increased the accessible pressure range for structural research up to several dozens of gigapascals. We have developed a methodology to perform single crystal X-ray diffraction experiments in double-side laser-heated DACs and demonstrated that the solution of crystal structures, their refinement, and accurate measurements of the thermal equation of state of metals, oxides, and silicates from single crystal diffraction data are possible in a megabar pressure range at temperatures of thousands degrees. Particular attention is paid to the in situ study of silicate perovskite (Pv) at extreme conditions. By tracking the changes of crystallographic parameters at pressures above 120 GPa and temperatures up to 2200 K, we found that (a) there is no a spin state crossover in ferric iron occupying the bicapped trigonal prism (``A'') crystallographic site, and (b) ferric iron does not enter the octahedral (``B'') site at any conditions of our experiments. We demonstrate that incorporation of ferric iron and aluminum significantly increases the compressibility of Pv and show that the oxidation state of iron is a critical parameter for interpretation of seismic tomography data. [Preview Abstract] |
Wednesday, July 10, 2013 9:45AM - 10:00AM |
O5.00003: Evaluation of Elastic Properties of Iron in Diamond Anvil Cell by a Laser Ultrasonics Technique up to 52 GPa Alexey Semeno, Pavel Zinin, Katherine Burgess, Vitali Prakapenka In this report, we present results on measurements of shear and longitudinal wave velocities in iron under high pressure up to 52 GPa. The measurements were conducted using laser ultrasonics (LU) in diamond anvil cells (DAC), LU-DAC technique.\footnote{N. Chigarev, P. Zinin, L. Ming, G.Amulele, A. Bulou, V. Gusev, \textit{Appl. Phys. Lett.} 93 181905 (2008).} The iron sample is attached to the lower diamond and separated from the upper diamond by NaCl. The way the sample is loaded in DAC allows measurements of acoustical wave velocities with two different configurations: acoustic waves propagated inside the specimen are excited and detected by a pump laser and a probe laser located (a) on the same side of the specimen or (b) on the opposite sides of the specimen. We found that the signals detected at the configuration (a) are similar to those measured without NaCl and show the arrival time of the longitudinal and shear waves.\footnote{Chigarev, \textit{Appl. Phys. Lett.}} In addition to skimming and bulk acoustic modes observed and analyzed in a previous study,\footnote{Chigarev, \textit{Appl. Phys. Lett.}} the detection of head waves is reported. In configuration (b), the signal shows arrival of the longitudinal wave and a set of the Lamb modes. [Preview Abstract] |
Wednesday, July 10, 2013 10:00AM - 10:15AM |
O5.00004: In-situ XRD of iron at megabar pressures with short laer pulses Zuzana Konopkova, Alexander Goncharov, Hanns-Peter Liermann, Wolfgang Morgenroth, Jan Torben Delitz, Vitali Prakapenka Recent improvements and growing technical capabilities of synchrotron sources enable us to investigate matter on shorter time scales, partially bypassing problems with sample contaminations and reaching increasingly higher temperatures at higher pressures. High quality x-ray diffraction data are nowadays feasible to obtain in several tens of milliseconds thanks to the high photon flux and efficient large area detectors. In-situ XRD experiments were conducted at the Extreme Conditions Beamline, P02.2, PETRAIII, Hamburg. The short laser pulses keep the heating time at minimum, which proves to be less destructive to the diamonds and the sample. We have followed the above strategy to study iron at megabar pressures. Measuring diffraction of iron at Earth's core conditions is technically difficult to achieve, which leads to contradictory results. We observe re-crystallization at highest temperatures and appearance of reflections with a large thermal shift. Further studies on melting and phase transitions will be conducted on iron and other metals in the near future. [Preview Abstract] |
Wednesday, July 10, 2013 10:15AM - 10:45AM |
O5.00005: Melting and vibrational properties of planetary materials under deep Earth conditions Invited Speaker: Jennifer M. Jackson The large chemical, density, and dynamical contrasts associated with the juxtaposition of a liquid iron-dominant alloy and silicates at Earth's core--mantle boundary (CMB) are associated with a rich range of complex seismological features. For example, seismic heterogeneity at this boundary includes small patches of anomalously low sound velocities, called ultralow-velocity zones. Their small size (5 to 40 km thick) and depth (about 2800 km) present unique challenges for seismic characterization and geochemical interpretation. In this contribution, we will present recent nuclear resonant inelastic x-ray scattering measurements on iron-bearing silicates, oxides, and metals, and their application towards our understanding of Earth's interior. Specifically, we will present measurements on silicates and oxide minerals that are important in Earth's upper and lower mantles, as well as iron to over 1 megabar in pressure. The nuclear resonant inelastic x-ray scattering method provides specific vibrational information, e.g., the phonon density of states, and in combination with compression data permits the determination of sound velocities and other vibrational information under high pressure and high temperature. For example, accurate determination of the sound velocities and density of chemically complex Earth materials is essential for understanding the distribution and behavior of minerals and iron-alloys with depth. The high statistical quality of the data in combination with high energy resolution and a small x-ray focus size permit accurate evaluation of the vibrational-related quantities of iron-bearing Earth materials as a function of pressure, such as the Gr\"{u}neisen parameter, thermal pressure, sound velocities, and iron isotope fractionation quantities. Finally, we will present a novel method detecting the solid-liquid phase boundary of compressed iron at high temperatures using synchrotron M\"{o}ssbauer spectroscopy. Our approach is unique because the dynamics of the iron atoms are monitored. This process is described by the Lamb-M\"{o}ssbauer factor, which is related to the mean-square displacement of the iron atoms. We will discuss the implications of our results as they relate to Earth's core and core-mantle boundary regions. [Preview Abstract] |
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