Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session H31: Focus Session: Materials at High Pressure I: Molecular and Simple Materials |
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Sponsoring Units: DMP GSCCM DCOMP Chair: Choong Shik Yoo, Washington State University Room: C145 |
Tuesday, March 22, 2011 8:00AM - 8:12AM |
H31.00001: Structural investigation and shock Hugoniot calculations of methane under high temperatures and pressures Benjamin Sherman, Burkhard Militzer, Hugh Wilson, Dayanthie Weeraratne The behavior of methane under pressures and temperatures spanning 0.02-7.75 Mbar and 300-30,000 K was studied using density functional molecular dynamics. The structural properties of fluid and crystalline methane were analyzed with simulations at various (P,T) conditions. These simulations were also used to calculate the shock Hugoniot curves of methane for a range of initial densities between 0.4-0.57 g/cc. These curves allow us to make predictions of state and phase that correspond to future methane shock experiments. [Preview Abstract] |
Tuesday, March 22, 2011 8:12AM - 8:24AM |
H31.00002: Proton Exchange Reactions in Deuterium Water Mixtures Gustav Borstad, Choong-Shik Yoo Binary mixtures of water and hydrogen under pressure are of interest both as fundamental systems in physics and chemistry and due to their applicability to fuel cells. Their behaviors at extreme pressures and temperatures are also of significance to understanding the interaction of chemical species in the interiors of giant gas planets and other planetary objects. In this talk, we will present high-pressure Raman data of deuterium water mixtures, which provides both kinetic information regarding the proton exchange reactions and the structure of deuterium in the mixtures. [Preview Abstract] |
Tuesday, March 22, 2011 8:24AM - 8:36AM |
H31.00003: Zero-Temperature Structures of Atomic Metallic Hydrogen Jeffrey McMahon, David Ceperley Since the first prediction of an atomic metallic phase of hydrogen by Wigner and Huntington over 75 years ago, there have been many theoretical efforts aimed at determining the crystal structures of the zero-temperature phases. We present results from ab initio random structure searching with density functional theory performed to determine the ground state structures from $500$ GPa to $5$ TPa. We estimate that molecular hydrogen dissociates into a monatomic body-centered tetragonal structure near $500$ GPa ($r_s = 1.225$), which then remains stable to $2.5$ TPa ($r_s = 0.969$). At higher pressures, hydrogen stabilizes in an $...ABCABC...$ planar structure that is remarkably similar to the ground state of lithium, which compresses to the face-centered cubic lattice beyond $5$ TPa ($r_s < 0.86$). Our results provide a complete ab initio description of the atomic metallic crystal structures of hydrogen, resolving one of the most fundamental and long outstanding issues concerning the structures of the elements. [Preview Abstract] |
Tuesday, March 22, 2011 8:36AM - 8:48AM |
H31.00004: Phase Diagram of Carbon Dioxide at High Pressure and Temperatures: Implications to the Deep Carbon Cycle Choong-Shik Yoo, Amartya Sengupta Carbon dioxide is an important terrestrial volatile often considered to exist in the deep interior of the Earth. The phase diagram of carbon dioxide is critical to validate such hypothesis. In this study, we will present the phase diagram of carbon dioxide including the most recent finding of coesite-like carbon dioxide, a missing analog to SiO$_{2}$, address several controversies in terms of phase metastabilities and thermal path dependent transitions, and discuss about the implication to the deep carbon cycle. [Preview Abstract] |
Tuesday, March 22, 2011 8:48AM - 9:00AM |
H31.00005: Structural and optical properties of liquid CO$_2$ up to 1 terapascal Brian Boates, Sebastien Hamel, Eric Schwegler, Stanimir Bonev The properties of liquid CO$_2$ have been studied through first-principles molecular dynamics simulations in the pressure-temperature range of 0-1 TPa and 200-100,000 K. The resulting equation of state data is used to predict shock Hugoniots for several initial conditions. Comparison with available experimental data up to 70 GPa is excellent. We find a gradual phase transition characterized by the destabilization of CO$_2$ molecules and the formation of other molecular compounds. The liquid phase diagram is divided into several regimes based on a thorough analysis on changes in bonding, structural properties, and chemical composition. Calculations of optical properties such as conductivity and reflectivity will also be discussed. [Preview Abstract] |
Tuesday, March 22, 2011 9:00AM - 9:12AM |
H31.00006: Density Functional Theory (DFT) simulations of CO2 under shock compression and design of liquid CO2 experiments on Z T. R. Mattsson, L. Shulenburger, S. Root, K. R. Cochrane Quantitative knowledge of the thermo-physical properties of CO2 at high pressure is required to confidently model the structure of gas-giants like Neptune and Uranus and the deep carbon cycle of the earth. DFT based molecular dynamics has been established as a method capable of yielding high fidelity results for many materials, including shocked gases, at high pressure and temperature. We predict the principal Hugoniot for liquid CO2 up to 500GPa. Our simulations also show that the plateau in shock pressure identified by Nellis and co-workers [1] is the result of dissociation. At low temperatures we validate the DFT results by comparing with diffusion Monte Carlo calculations. This allows for a more accurate determination of the initial conditions for the shock experiments. We also describe the design of upcoming flyer-plate experiments on the Z-machine aimed at providing high-precision shock compression data for CO2 between 150 and 600 GPa. [1] W. Nellis, et. al. , J. Chem. Phys. {\bf 95}, 5268 (1991). [Preview Abstract] |
Tuesday, March 22, 2011 9:12AM - 9:48AM |
H31.00007: Novel phases of simple substances at megabar pressures Invited Speaker: Under megabar pressures solids can be strongly compressed: volume of solid hydrogen decreases in $\sim $20 times, even diamond is 1.5 fold compressed at achievable pressures of $>$300 GPa. This dramatically changes interatomic distances in materials eventually leading to metallization in a number of presenting substances. Metals under compression supposedly remain in metallic state. But at high densities the core electrons come in to play and the electronic structure significantly departs from the simple metal as it was demonstrated for lithium. We present an ultimate case: sodium - simple metal - becomes transparent at pressures of $\approx $200 GPa transforming into ionic- electride-like state. We will present also our recent studies on nitrogen and nitrogen-rich materials: ammonia, azides and others, and progress on studies at pressures $\sim $400 GPa. [Preview Abstract] |
Tuesday, March 22, 2011 9:48AM - 10:00AM |
H31.00008: Diamond as a high pressure gauge up to 2.7 MBar Natalia Dubrovinskaia, Leonid Dubrovinsky, Razvan Caracas, Michael Hanfland Diamond anvil cell (DAC) technique has become a very important method of probing materials behaviour under pressure in various fields of research ranging from physics to biology and geoscienses. Optical methods of pressure determining in DAC experiments are based on fluorescent markers or calibrated pressure dependence of the Raman shift of suitable materials. Diamond has been since long recognised as a good pressure marker in experiments conducted in a diamond anvil cell. It is stable at ultra-high pressures that allows one to use the pressure dependence of the Raman frequency of the LTO optical phonon of diamond as a pressure gauge. A pressure gauge is a key issue of any high pressure experiment in a diamond anvil cell. Here we present a method of \textit{in situ} synthesis of microcrystals of diamond that can be further used as a pressure standard in course of the same DAC experiment. Calibration curve of the Raman shift \textit{vs} pressure is extended up to 270 GPa and experimental results are compared with those of \textit{ab initio} calculations. [Preview Abstract] |
Tuesday, March 22, 2011 10:00AM - 10:12AM |
H31.00009: High-pressure and high temperature deformation studies of polycrystalline diamond Xiaohui Yu With Vicker's hardness 120 GPa, shear modulus 535 GPa, diamond is the hardest material known to mankind. However, because diamond is difficult to deform, little is known with regard to its constitutive properties such as yield strength. In this work, we present results obtained at NSLS using deformation-DIA on polycrystalline diamond at different P-T conditions. As expected, even at total strains up to 20{\%}, we did not observe the yield point of diamond at room temperature and a confining pressure of 4 GPa. However, for deformation at 1000 and 1200 $^{\circ}$C, we observed an plastic flow of diamond at total strains of 10{\%} and 5{\%}, respectively, indicating that diamond weakens rapidly when temperature is over 1000 $^{\circ}$C. We further derived the micro stress of diamond from peak width analysis, and found that the micro and macro stresses show similar variations with total strain at both room temperature and 1000 $^{\circ}$C. However, at 1200 $^{\circ}$C, the micro stress remains constant in entire deformation, indicating that stress is uniformly distributed within diamond particles at 1200 $^{\circ}$C. We also carried out SEM studies on the recovered samples to investigate the miscrostructures, and find that the grain size of diamond decreases substantially during the deformation, from the initial microns to sub-microns for the room temperature deformation, however, almost doesn't change for the 1200 $^{\circ}$C. [Preview Abstract] |
Tuesday, March 22, 2011 10:12AM - 10:24AM |
H31.00010: New primary pressure calibrants for high pressure and temperature scale: SiC-3C and cBN are possible candidates Kirill Zhuravlev, Alexander Goncharov, Vitali Prakapenka Since the invention of a diamond-anvil cell, various high-pressure scales for in situ pressure measurements have been realized. Ruby-based pressure scale (Mao et al., 1986) is the best known and high-pressure scientific community has been using it for over two decades. However, it has limited use at elevated temperatures, due to the weakening and broadening of the ruby fluorescence line. The recent developments in the field of high temperature, high pressure physics and geophysics require some alternative pressure scale, capable of measuring pressures at temperatures up to 3000 K. Cubic boron nitride (cBN) was recently proposed as the possible pressure calibrant. It has been suggested that the simultaneous use of x-ray diffraction to measure density and Brillouin spectroscopy to obtain elastic properties of the crystal can be used to construct the pressure scale independent of any other pressure standards. However, the acoustic velocities of cBN are very close to those of diamond and, therefore, are hard to resolve in experiment in diamond-anvil cell. Another possible primary pressure calibrant is cubic silicon carbide (SiC-3C). We performed single crystal x-ray diffraction and Brillouin spectroscopy up to 1 Mbar in pressure at room temperature in the diamond-anvil cell and show that cBN and SiC-3C, indeed, can be used in constructing reliable and accurate high-pressure, high-temperature scale. [Preview Abstract] |
Tuesday, March 22, 2011 10:24AM - 10:36AM |
H31.00011: Formation and superconductivity of hydrides under pressure Duck Young Kim, Ralph H. Scheicher, Chris J. Pickard, Richard J. Needs, Rajeev Ahuja Hydrogen is the lightest and smallest element in the periodic table. Despite its simplest electronic structure, enormous complexity can arise when hydrogen participates in the formation of solids. Pressure as a controllable parameter can provide an excellent platform to investigate novel physics of hydrides because it can induce structural transformation and even changes in stoichiometry accompanied with phenomena such as metallization and superconductivity. In this presentation, we will briefly overview contemporary high-pressure research on hydrides and show our most recent results on predicting crystal structures of metal hydrides under pressure using ab initio random structure searching. Our findings allow for a better understanding of pressure-induced metallization/superconductivity in hydrides which can help to shed light on recent observations of pressure-induced metallization and superconductivity in hydrogen-rich materials. [Preview Abstract] |
Tuesday, March 22, 2011 10:36AM - 10:48AM |
H31.00012: Mechanical properties of icosahedral boron carbide explained from first principles Roman Raucoules, Nathalie Vast, Emmanuel Betranhandy, Jelena Sjakste An exhaustive DFT study of the structural defects of icosahedral B$_{4}$C and of their behavior under high pressure has been performed. Among the possible atomic structures, the lowest value of the formation energy has been found for the \textit{polar} model B$_{4}$C$^{P}$, which consists of one distorted icosahedron and of one CBC chain. This result, together with the inspection of the vibrational and NMR spectra, has proved that B$_{4}$C$^{P}$ is the proper structural model for B$_{4}$C.[1,2] Consequently, B$_{4}$C$^{P}$ has been used as a matrix to isolate the defects. The native defects have been identified and shown to be energetically stable at high pressure. Most vacancy locations in B$_{4}$C$^{P}$ are found to be energetically unstable and only a boron vacancy in the CBC chain is stable. A cluster of this vacancy is shown to induce a dynamical instability of the icosahedra when the pressure is increased. The dynamical failure of shocked B$_{4}$C [3] is attributed to the increase in the concentration of these unstable vacancies under plastic deformation. 1. R. Lazzari, N.Vast, J.M. Besson, S. Baroni and A. Dal Corso, Phys. Rev. Lett. 83 (1999) 3230. 2. F. Mauri, N. Vast and C.J. Pickard, Phys. Rev. Lett. 87 (2001) 085506. 3. T. Vogler, W. Reinhart and L. Chhabildas, J. Appl. Phys. 95 (2004) 4173. [Preview Abstract] |
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