Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session W23: Focus Session: Extreme Conditions and High Pressure IV: Equations of State and Dynamics |
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Sponsoring Units: DCOMP GSCCM Chair: Kyle Caspersen, Lawrence Livermore National Laboratory Room: 325 |
Thursday, March 19, 2009 11:15AM - 11:27AM |
W23.00001: Pressure induced structural transitions in the potential hydrogen storage compound NH$_{3}$BH$_{3}$ Ravhi Kumar, Jianzhong Zhang, Monika Hartl, Zhijun Lin, Sven Vogel, Luke Daemen, Andrew Cornelius, Malcolm Nicol, Yushen Zhao Ammonia borane has received much attention in recent years as it is reported to have up to 19.6 wt {\%} of hydrogen [1-2]. Hydrogen is released in a three step process when heated above 100$^{\circ}$C. To understand the structural stability of this compound under compression, we have performed high pressure angle dispersive x-ray diffraction experiments up to 27 GPa using synchrotron x-rays at HPCAT, Advanced Photon Source. Two successive pressure induced structural phase transitions were observed. The ambient tetragonal structure transforms to an orthorhombic structure around 1.2 GPa and then to another high pressure phase above 8 GPa. Complementary neutron diffraction experiments performed up to 5 GPa at LANSCE are in good agreement with the x-ray results. The structural details of the high pressure phases will be presented.\\[4pt] [1] Z. Xiong et al., Nature, 7 (2008) pp 034508\\[0pt] [2] J.B.Yang etal., Appl.Phys.Lett, 92 (2008) pp 091916 [Preview Abstract] |
Thursday, March 19, 2009 11:27AM - 11:39AM |
W23.00002: Pressure-dependent structures of amorphous red phosphorus and the origin of first sharp diffraction peaks. Joseph Zaug, Alan Soper, Simon Clark Characterizing the nature of medium range order (MRO) in liquids and disordered solids is important for understanding their structure and transport properties. However, accurately portraying MRO, as manifested by the first sharp diffraction peak (FSDP) in neutron and X-ray scattering measurements, has remained elusive for more than 80 years. Here, using X-ray diffraction of amorphous red phosphorus (a-rP) compressed to 6.30 GPa, supplemented with micro-Raman scattering studies, we build three-dimensional structural models consistent with the diffraction data. We discover that the pressure dependence of the FSDP intensity and line position can be quantitatively accounted for by a characteristic void distribution function, defined in terms of average void-size, void-spacing, and void-density. This work provides a template to unambiguously interpret atomic and void-space MRO across a broad range of technologically promising network-forming materials. [Preview Abstract] |
Thursday, March 19, 2009 11:39AM - 11:51AM |
W23.00003: ABSTRACT WITHDRAWN |
Thursday, March 19, 2009 11:51AM - 12:03PM |
W23.00004: First-principles calculation of lattice anharmonicity and lattice thermal conductivity of MgSiO3 perovskite Xiaoli Tang, Abby Kavner, Jianjun Dong MgSiO3 perovskite (Mg-pv) is likely the most abundant material in the Earth's lower mantle, and its thermal conductivity at the high pressure and high temperature conditions of the Earth's interior plays an important role in governing heat transport and thus the whole Earth evolution. Measurement of the lattice thermal conductivity ($\kappa )$ of this important material is still not available at lower mantle conditions. We will present a theoretical study of $\kappa $ for Mg-pv calculated with a parameter-free method which combines first-principle techniques, quantum scattering theory, and kinetic transport equation. We have explicitly calculated the pressure dependence of both harmonic phonon spectra and the third order lattice anharmonicity tensors. A preliminary analysis based on the single relaxation time approximation suggests that the increase of phonon frequencies at high pressures contributes to the increase of $\kappa $ at the rate of $1\% GPa^{-1}$ at 1000K and $1.3\% GPa^{-1}$ at 3000K. The pressure dependence of phonon relaxation time and its implication for the pressure dependence of $\kappa $ will also be discussed. [Preview Abstract] |
Thursday, March 19, 2009 12:03PM - 12:15PM |
W23.00005: Theoretical study of pressure dependence of lattice thermal conductivity in MgO Jianjun Dong, Xiaoli Tang We have recently developed a computation method that combines first-principles methods and transport theories to directly calculate lattice thermal conductivities for MgO at high pressure and high temperature conditions. Within the simple single-phonon-lifetime approximation, we estimate that the blueshifts in phonon frequencies lead to an increase of conductivity at high pressure at a rate of 1.3{\%}GPa$^{-1}$ (300K). A further calculation using quantum scattering theory shows that the anharmonicity-induced phonon scattering rate decreases at high pressure. The estimated pressure effect related to the phonon lifetime increase is comparable to that due to the frequency blueshifts. Our final calculation results will be discussed with comparison to available experiment data and the damped-harmonic-oscillator-phonon-gas model. [Preview Abstract] |
Thursday, March 19, 2009 12:15PM - 12:27PM |
W23.00006: Effects of Ionizing Radiation on Capacitors Harold P. Hjalmarson, Rudolph J. Magyar, Paul S. Crozier, E. Frederick Hartman Irradiation of an insulator by energetic ionizing radiation creates hot electrons and holes. These species cool by creating additional hot electrons and holes. In this presentation, the consequences of these hot carriers will be computed using a continuum transport method in which the carriers are assumed to be described by a quasi-equilibrium temperature much larger than the lattice temperature. The electrical effects of carrier recombination at defects for simple capacitors under irradiation will be described. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin company, for the United States Department of Energy under contract DE-AC04-94AL85000. [Preview Abstract] |
Thursday, March 19, 2009 12:27PM - 12:39PM |
W23.00007: Quasi-isentropic Compression Waves Generated by Shock Waves into Sapphire W. J. Nellis, G. I. Kanel, S. V. Razorenov, A. S. Savinykh, A. M. Rajendran For sixty years it has tacitly been assumed that a shock wave incident on a material will propagate as a shock wave in that material. Between 15 and 80 GPa a shock wave cannot propagate in sapphire, the first material demonstrated not to have a Hugoniot. Wave profiles of sapphire crystals with three orientations and two thicknesses were measured at incident shock stresses of 14, 24 and 87 GPa. 14 GPa generates elastic shocks that are overdriven at $\sim $90 GPa. Elastic-precursor decay occurs at 24 and 87 GPa. At 24 GPa all three orientations have plastic-compression waves with rise times of 200-300 ns. Long rise times are probably caused by strong bonds that break heterogeneously and statistically over a relatively long time interval. This slow damage-induced increase in pressure causes quasi-isentropic compression. Since the Hugoniot and isotherm of sapphire are essentially coincident up to 340 GPa, dissipative energy probably goes primarily into entropy of disordering the crystal rather than temperature. [Preview Abstract] |
Thursday, March 19, 2009 12:39PM - 12:51PM |
W23.00008: Micron scale simulations of a Kelvin-Helmholtz instability: a direct comparison between molecular dynamics and Navier-Stokes hydrodynamics. Kyle Caspersen, Robert Rudd, David Richards, Jim Glosli, William Cabot, Paul Miller, Fred Streitz The modeling of hydrodynamic phenomena has largely been the purview of continuum mechanics, such as through the solution of the Navier-Stokes equations. Nevertheless, at small length scales, where atomistic effects become important, it is not clear that this continuum approach provides a complete description of fluid behavior. To understand the effects of atomistics, we have performed a 9 billion atom quasi-2D molecular dynamics simulation, and the corresponding Navier-Stokes hydrodynamic simulation, of an interface of copper and aluminum in a strong shear layer. The applied shear flow of 2 km/s produces complex phenomena associated with a Kelvin-Helmholtz (KH) instability. In this presentation we compare and contrast the initiation and early evolution of the KH instability modeled both by molecular dynamics and continuum hydrodynamics. [Preview Abstract] |
Thursday, March 19, 2009 12:51PM - 1:03PM |
W23.00009: Transition of deformation modes in Shocked Tantalum Luke Hsiung Shock-induced twinning and $\alpha $ (bcc) $\to \quad \omega $ (hexagonal) phase transition in tantalum, which exhibits no clear solid-state phase transformation under hydrostatic pressure conditions, have been investigated. Since the domains of deformation twin and $\omega $ phase were frequently observed in regions containing high-density screw dislocations without dislocation cell structures, it is suggested that the shock-induced shear transformations (twinning and phase transformation) occur as alternative deformation modes to accommodate insufficient dislocation flow resulting from the exhaustion of dislocation multiplication when dynamic recovery processes for dislocation annihilation and cell formation become largely suppressed under dynamic pressure conditions. A physical mechanism based upon the overlapping of closely spaced dislocation loops nucleated from a jogged screw dislocation is proposed to rationalize the shock-induced shear transformations. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Thursday, March 19, 2009 1:03PM - 1:15PM |
W23.00010: Hydrogen at Extreme Conditions Subramanian Natarajan, Alexander Goncharov, Somayazulu Maddury, Russell Hemley Vast regions of the P-T phase diagram of H$_{2}$, especially in the high P-T region, remain to be explored for melting behavior and exotic phenomena related to disassociation of the H$_{2}$ molecule, metallicity and superconductivity. In recent years, few experiments employing either laser-heating or resistive heating techniques in conjunction with in situ spectroscopic experiments using Diamond Anvil Cells (DAC) have been reported attempting to address some of these. A key problem that faces experimenters is to confine the hot and reactive H$_{2}$ in the small DAC sample chamber at high pressures long enough to make meaningful measurements of physical properties. Recently, we have made considerable progress in confining hot and dense hydrogen while not compromising on the ability to make spectroscopic measurements using a complex sample assembly. With this, it has been possible to perform in situ Raman spectroscopy on H$_{2}$ and D$_{2}$ while simultaneously doing double-sided laser heating at P-T conditions of more than 1Mbar and 1500K. Typically, we are now able to perform laser heating and in situ Raman spectroscopy over several heating/cooling cycles without loss of H$_{2}$ in the Mbar range. Results of these experiments will be presented; along with details of the methodology we adopted to successfully confine hot and dense hydrogen. [Preview Abstract] |
Thursday, March 19, 2009 1:15PM - 1:27PM |
W23.00011: An accurate high pressure scale from quantum Monte Carlo Kenneth Esler, R.E. Cohen, Burkhard Militzer, Jeongnim Kim We have developed a fundamental high-temperature and high-pressure scale based on cubic boron nitride (cBN) using a combination of Quantum Monte Carlo (QMC) for the static contribution along with density functional perturbation theory (DFPT) for the thermal pressure. The anharmonic Raman frequency was determined as a function of pressure by solving the Schrodinger equation for the vibrational well determined using QMC with the frozen phonon method. The use of cBN as a pressure scale has a number of advantages. Unlike ruby, its structure is highly constrained by symmetry and stable well beyond 100 GPa, and it has a well-separated Raman spectrum with sufficient pressure dependence to allow accurate pressure calibration. While the cBN EOS from density functional theory (DFT) gives reasonable agreement with experiment, the results from different approximate functionals disagree. Quantum Monte Carlo is a first principles simulation method which circumvents approximate functionals and is widely regarded to provide the most accurate predictions of the properties of solids available. We utilize state-of-the-art QMC methods to obtain the static EOS with the QMCPACK code. We include a novel correction based on all-electron wave functions to eliminate pseudopotential error. [Preview Abstract] |
Thursday, March 19, 2009 1:27PM - 1:39PM |
W23.00012: Softening of ultra-incompressible CrN at high pressure Francisco Rivadulla, Manuel Banobre, Alberto Pineiro, Victor Pardo, Daniel Baldomir, Arturo Lopez-Quintela, Jose Rivas We report a dramatic softening of CrN above 1.5 GPa, (the bulk modulus decreasing from K$_{0}$=413(20) GPa to 243(10) GPa) associated to a structural transition. From the structural and magnetic data under pressure, and ab-initio calculations we suggest that this effect is purely electronic, driven by the proximity of the ionic Cr-Cr bond to itinerant electron limit. Our results help to understand fundamental aspects of the chemical bond that gives superhard materials their superior al properties, and could be useful to preserve the mechanical properties of CrN. [Preview Abstract] |
Thursday, March 19, 2009 1:39PM - 1:51PM |
W23.00013: Correlating cation coordination, stiffness, phase transition pressures, and smart materials behavior in metal phosphates Dmitry Shakhvorostov, Nicholas Mosey, Yang Song, Peter Norton, Martin Mueser In this study, we present X-ray diffraction data on zinc- and calcium phosphates. The experiments reveal that low-coordinated zinc phosphates are relatively soft at ambient conditions but stiffen dramatically with pressure, p, exhibiting smart materials behavior, while high-coordinated zinc and calcium phosphates have higher initial bulk moduli and stiffen considerably less rapidly with increasing p. All systems amorphize when their bulk modulus reaches a value near 210~$\pm$~40 GPa, where the precise value depends on chemical details, indicating that phosphate networks become unstable when their bulk modulus reaches that value. Our ab initio simulations of zinc $\alpha$-phosphate support the idea that the elastic properties are controlled by the motion of rigid phosphate units, which becomes more hindered under densification, with or without increasing cation coordination. It is discussed how these results may explain why low-coordinated zinc phosphates are good anti-wear agents. [Preview Abstract] |
Thursday, March 19, 2009 1:51PM - 2:03PM |
W23.00014: Novel Numerical Computations for the Equation of State of Hard Particle Systems from Gaseous to Extreme High Densities Uduzei Edgal A special form of the ``Reduced Monte Carlo Scheme'' (RMCS) used for numerical computation of the EOS of the hard particle system (2D and 3D cases) will be discussed. A major advantage of the numerical scheme is that it does not lead to difficulties with meta-stable states as do traditional MC methods. In particular, RMCS calculations (in the special form) provide results from the lowest (fluid phase) to the highest (solid phase) densities which show a first order phase transition in the hard particle system [Preview Abstract] |
Thursday, March 19, 2009 2:03PM - 2:15PM |
W23.00015: X-ray diffraction of electrodeposited nanocrystalline Ni under high-pressure Christian Grant, Jonathan Crowhurst, Tom Arsenlis, Eduardo Bringa, Morris Wang, James Hawreliak, Peter Pauzauskie, Simon Clark We studied the compressibility of monolithic fully-dense electrodeposited nanocrystalline Ni (29 nm grain size) under both quasi-hydrostatic and non-hydrostatic conditions up to a nominal pressure of 50 GPa using angle-dispersive x-ray diffraction. We obtained an equation of state consistently and unambiguously from each measured reflection. The apparent bulk modulus measured under non-hydrostatic conditions is larger than that of the corresponding coarse grained-material under either type of compression, but is nearly the same when measured under quasi-hydrostatic conditions. Our results suggest that the strength, but not the bulk modulus, of 29 nm nanocrystalline Ni is enhanced relative to its coarse-grained counterparts. [Preview Abstract] |
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