Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session B11: High Pressure I |
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Sponsoring Units: DCMP DMP Chair: Matteo Cococcione, MIT Room: LACC 153C |
Monday, March 21, 2005 11:15AM - 11:27AM |
B11.00001: Boron a frustrated element: ab-initio study of pressure induced amorphization Tadashi Ogitsu, Francois Gygi, Giulia Galli At ambient conditions, boron exhibits the most complex structure of all elemental solids, with an intricate arrangement of interconnecting icosahedra and more than 300 atoms per unit cell. It is the only element purified in significant quantities whose ground state structure has not been fully determined. We have performe ab-initio study of boron at ambient condition and under pressure. At low P and temperature, our results favor a quasi-ordered, crystalline ground state with an even number of atoms per unit cell (320) and a finite density of states at the Fermi level. Due to the highly localized nature of these states, boron turns out to be non conductive, in agreement with experiment. At about 100 GPa, we observe an order-to-disorder transition, which occurs by a series of hierarchical structural changes. Contrary to intuition based on bond strength arguments, the ``short,'' inter-icosahedral bonds are broken first, followed by a partial rupture of icosahedral units with ``longer'' bonds, eventually leading to full disruption of long range order, consistent with recent measurements. Above 120 GPa, we find a notable increase in electronic conductivity, due to delocalization of electronic states, yielding a poor metallic state. [Preview Abstract] |
Monday, March 21, 2005 11:27AM - 11:39AM |
B11.00002: Mechanical and thermodynamic properties of solid Zirconium using a tight-binding approach Ilan Schnell, Matthew Jones, Sven Rudin, Robert Albers We use a tight-binding model that is fit to ab-initio DFT-GGA electronic-structure calculations for Zirconium. We will address difficulties involved with the fitting procedure and give zero-temperature results for elastic constants, force constants, and phonons. It turns out that the force constants obtained from our model are rather long-ranged. Within the quasi-harmonic approximation, we calculate phonon spectra for different crystal structures and at different pressures, allowing us to evaluate the Gibbs free energy as a function of pressure and temperature. We calculate parts of the phase diagram and other material properties, such as specific heat, and compare these to experimental data. [Preview Abstract] |
Monday, March 21, 2005 11:39AM - 11:51AM |
B11.00003: Universal transition state and transition path for the high-pressure zinc blende to rocksalt phase transition Maosheng Miao, Walter Lambrecht Although the high-pressure zinc blende (ZB) to rocksalt (RS) structural transition has been studied intensively in many experiments and theories, the understanding of the kinetics of this process, especially of its the transition state (TS), the saddle point on the transition path, is still incomplete. We studied the TS and energetics along a previously introduced low barrier orthorhombic transition path of the ZB to RS transition for several semiconductors, including II-VI and III-V compounds and group-IV elemental semiconductors using a first-principles full-potential linearized muffin-tin orbital method. The path is defined by the relative sublattice position and the lattice constants are allowed to relax in response to this chosen independent variable. We found that: 1) the location and the geometry of the TS are identical for all the semiconductors investigated; 2) the lattice constants and the scaled volume vary in a universal manner along the path for all the semiconductors; 3) the cosine function of the relative sublattice position can be used as an order parameter for expanding the energy associated with the the phase transition. A Landau like model for reconstructive phase transition with changing periodicity shows that the position of the transition state does not depend on the chemical components of the semiconductors. [Preview Abstract] |
Monday, March 21, 2005 11:51AM - 12:03PM |
B11.00004: Searching for viable transition paths of pressure driven phase transition in solid xenon: First-principle study Eunja Kim Pressure induced structural transformation in solid xenon has been investigated using a first-principles calculation. Enthalpy calculation confirms that the fcc-to-hcp transformation begins around 5 GPa and finishes up around 70 GPa. We propose two transformation pathways in solid xenon such as a stacking disorder growth pathway at low pressure (Path-I) and an orthorhombic distortion pathway followed by atomic rearrangements at high pressure (Path-II). Delicate interplay of enthalpy and energy barrier will be discussed to explain the underlying mechanism of how solid xenon selects the proper transformation pathways under pressure. [Preview Abstract] |
Monday, March 21, 2005 12:03PM - 12:15PM |
B11.00005: Classical Potential Describes Martensitic Phase Transformations in Titanium Thomas Lenosky, Richard Hennig, John Wilkins, Dallas Trinkle, Sven Rudin Titanium is technologically important for aerospace applications and scientifically interesting as it displays martensitic transformations between three crystal structures, hcp, bcc, and omega. We present an efficient classical interatomic potential for Ti that accurately describes all three phases and the structural transformations between them. The potential is of the modified embedded atom form employing cubic splines and incorporating angular bonding terms. The spline parameters are fit to a database of density-functional calculations of energies of different crystalline phases, forces, point defects, and elastic constants. We demonstrate the accuracy of the potential for all three crystalline phases by comparing the phonon spectra with experimental data and density-functional results. Constant stress molecular dynamics simulations determine the Ti phase diagram and thermal expansion as a function of pressure and temperature in good agreement with experimental data. This potential allows for accurate large-scale simulations of Ti under pressure including simulations of shock compression. [Preview Abstract] |
Monday, March 21, 2005 12:15PM - 12:27PM |
B11.00006: A Model for Heterogeneous Materials Undergoing Phase Transitions JeeYeon Plohr, Bradford Clements, Francis Addessio We develop a macroscopic model for a heterogeneous material undergoing a phase transition. Such a continuum-level material model, which is needed in practical engineering calculations, must faithfully reflect the micromechanical response of the constituent materials. Using the method of cells, which is a homogenization technique, we derive the constitutive properties of a composite material, part of which undergoes a phase transition. Specifically, we study tungsten heavy alloy (WHA), in which tungsten grains are dispersed within a low-melting-temperature alloy matrix. This material has desirable static properties as a penetrator, but melting in the matrix occurs during loading. Simulations with our model predicts the properties of WHA with different compositions, which can then be optimized. [Preview Abstract] |
Monday, March 21, 2005 12:27PM - 12:39PM |
B11.00007: Theoretical Analysis of Stress-Induced Structural Response of Cubic Crystals Beyond the Onset of Elastic Instability Hadrian Djohari, Jianhua Zhao, Frederick Milstein, Dimitrios Maroudas Determining the mechanical strength of crystalline materials requires elastic stability analyses for fundamental understanding of crystal large-strain deformation and failure. In this presentation, we report results of systematic elastic stability analyses in metallic crystals based on isostress molecular-dynamics simulations that capture in detail the mechanical, geometric, and kinetic aspects of stress-induced instabilities. Our analysis emphasizes bifurcations in the crystal structural response exhibited as the applied load is varied and atomic pattern formation characteristics beyond the instability onset. Results are presented for various cases of structural evolution under hydrostatic and uniaxial [100] and [111] loading for model crystals that have an fcc structure at equilibrium. The corresponding structural responses range from inhomogeneous structural transitions to fracture through decohesion and voiding. The observed instabilities are thermally activated and associated with vanishing or diminishing combinations of elastic moduli. [Preview Abstract] |
Monday, March 21, 2005 12:39PM - 12:51PM |
B11.00008: Ellipsometry of Shocked Crystals: Birefringence and Relaxation of LiF Reed Patterson, Jeffrey Nguyen, Neil Holmes Ellipsometry measurements on dynamically compressed materials present a novel technique for characterizing the behavior of materials at extreme conditions. Such measurements yield information about dielectric and strain properties which in turn provide insight into the dynamic behavior of materials, e.g.~plasticity, phase transitions, strength, crystal structure, etc. Previous ellipsometry measurements on shocked LiF at the two-stage light-gas gun at LLNL have shown strain-induced birefringence. In addition, these measurements suggest that LiF does not relax immediately from a uniaxially compressed state to the hydrostat, as suggested by recent x-ray data, but that there is a time scale associated with the relaxation of the crystal lattice following the shock. Coupling time-resolved optical measurements of the refractive indices with the stress tensor will allow us to develop a better understanding of the origin and kinetics of plasticity and phase transitions in addition to yielding valuable structural data on high-pressure high-temperature materials.\\ \\ This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48. [Preview Abstract] |
Monday, March 21, 2005 12:51PM - 1:03PM |
B11.00009: High Pressure Studies of PETN up to 74 GPa Michael Pravica, Krystyna Lapinska-Kalita, Hubertus Giefers, YongRong Shen, Malcolm Nicol, Maddury Somayazulu, Michael Hu We have studied the popular high explosive PETN (Pentaerythritol Tetranitrate ) using X-ray powder diffraction (up to 74 GPa) and X-ray energy-dispersive diffraction (up to 30 GPa), X-ray Raman Spectroscopy (up to 20 GPa), and Raman Spectroscopy (up to 50 GPa). All studies were carried out at room temperature. The X-ray studies were carried out at the HP-CAT beamline (16 ID-B, 16 BM-B and 16 ID-D) at the Advanced photon source (APS) at Argonne National Laboratory. We present evidence for two new phases of PETN above 5 GPa and above 10 GPa including an equation of state of the material. [Preview Abstract] |
Monday, March 21, 2005 1:03PM - 1:15PM |
B11.00010: Pressure dependence of the first-order Raman frequency in isotopically mixed diamond Alexander Goncharov, Hisao Kanda, Sergei Stishov We report the results of the Raman measurements under hydrostatic pressure to 12 GPa in isotopically mixed $^{12}$C$_{(1-x)}^{13}$C$_{x}$ (x=0.3 and 0.75) diamonds in the diamond anvil cell using helium as a pressure medium. The results show that the pressure dependences of isotopically mixed samples are stronger than that for almost isotopically pure natural diamond (x=0.011). We attribute this fact to the disorder effects that renormalizes the Raman frequency. We acknowledge the use of the CDAC facility in Geophysical Laboratory Carnegie Institution of Washington. SMS appreciates support from programs of Department of Physics of Russian Academy of Sciences. [Preview Abstract] |
Monday, March 21, 2005 1:15PM - 1:27PM |
B11.00011: High Pressure Structural Phase Transitions in Lithium Nitride Amy Lazicki, Choong-Shik Yoo, Warren Pickett, Richard Scalettar, Maddoury Somayazulu, Daniel Hausermann High pressure behaviors of Li$_{3}$N have been investigated by using synchrotron x-ray diffraction up to 200 GPa in a diamond anvil cell. We found that Li$_{3}$N undergoes a structural phase transition from a layered hexagonal to a close-packed cubic phase at 36-45 GPa with a large volume collapse of 8\%. The high-pressure cubic phase is stable up to at least 200 GPa, the maximum pressure applied in the present experiments. We have also carried out first principles calculations on the high-pressure phase and found good agreement between the calculated and measured EOS. These calculations further predict a widening of the band gap up to a volume compression of 33\% of the initial volume before the eventual collapse and metallization at a pressure of 7.9 TPa. The high-stability of wide-band gap Li$_{3}$N is, therefore, analogus to those of NaCl, MgO and Ne. This work has been supported by the LDRD-04-ERD-020 at the LLNL, University of California, under the auspices of the U.S. DOE under Contract No. W-7405-ENG-48 . [Preview Abstract] |
Monday, March 21, 2005 1:27PM - 1:39PM |
B11.00012: Commensurate N2-O2 Alloys at High Pressures Bruce Baer, Jae-Hyun Park Klepeis, Choong-Shik Yoo Several high pressure binary mixtures have been investigated over the past fifteen years. The phase diagrams of many of these systems have been shown to contain one or more van der Waals compounds. Often, the crystal structures of these compounds are quite unique from those of the parent pure compounds. In this talk we will look at the compounds formed by certain mixtures of nitrogen and oxygen at very high pressures. Compounds with oxygen content as high as 40{\%} suggest that there may be commensurate alloys that can be metallized in the diamond cell. The spectroscopy and crystal structures of these alloys also have important implications concerning the crystal structure of $\varepsilon $-O$_{2}$ and the presence of O$_{4}$ in pure oxygen at high pressure. This work has been supported by the LDRD and PDRP programs at Lawrence Livermore National Laboratory, University of California under the auspices of the U.S. Department of Energy under Contract No. W-7405-ENG-48. [Preview Abstract] |
Monday, March 21, 2005 1:39PM - 1:51PM |
B11.00013: High Pressure Synthesis of a New 0201 type Oxychloride High Tc Superconductor by ``Apical Oxygen Doping'' Q. Q. Liu, X. M. Qin, C. Q. Jin We present our recent research works on high pressure synthesis of high Tc superconductors in the alkaline earth copper oxychloride system of Sr$_{2}$CuO$_{2}$Cl$_{2}$, the isostructure compound with La$_{2}$CuO$_{4,}$ where the apical site relative to the [CuO2] plane is chlorine rather than the usual oxygen. Using the ``apical oxygen doping'' mechanism, i.e., partially substituting the oxygen for chlorine, we succeeded in synthesizing a new 0201 type superconductor Sr$_{2}$CuO$_{2+\delta }$Cl$_{2-x}$. Nearly single phase of Sr$_{2}$CuO$_{2+\delta }$Cl$_{2-x}$ superconductors were obtained, showing superconducting transition at 35 K for the as-prepared sample. [Preview Abstract] |
Monday, March 21, 2005 1:51PM - 2:03PM |
B11.00014: Impulsive stimulated scattering on metal and semiconductor interfaces under high pressure Eric Chronister, Bruce Baer, Masashi Yamaguchi Impulsive stimulated scattering (ISS) is used to measure the orientation dependence of surface acoustic wave velocities on crystalline metal and semiconductor surfaces. ISS coherently drives surface acoustic modes yielding a relatively large scattering efficiency [1]. ISS data is obtained continuously from the Rayleigh surface wave (RSW) branch through the pseudo RSW branch, which is typically not possible with classical Brillouin scattering. The ISS technique is found to be a robust non-contact method of probing the surface acoustic properties of metal and semiconductor crystalline interfaces. Orientationally resolved acoustic velocity data on crystal surfaces can be used to determine the bulk elastic constants of the material and ISS results were also found to be more robust than Brillouin scattering with respect to surface quality. At high pressure, the solid surface is in contact with a pressure-mediating fluid (nitrogen in this case), and the liquid-solid interface supports the propagation of a Sholte surface mode in addition to the generalized Rayliegh wave, both of which are resolved in the ISS power spectrum. 1] Rogers, Maznev, Banet, Nelson, Annu.Rev.Mater.Sci.30, 117, 2000. [Preview Abstract] |
Monday, March 21, 2005 2:03PM - 2:15PM |
B11.00015: Shear stresses in shock compressed covalent solids Ivan Oleynik, Sergey Zybin, Mark Elert, Carter White Shear stresses are the driving forces for the creation of both point and extended defects in crystals subjected to high pressures and temperatures. We report DFT results appropriate for shear stresses in shock compressed covalent solids such as diamond and silicon for three low-index crystallographic directions, $<$100$>$, $<$110$>$, $<$111$>$. The non-monotonic behavior of shear stresses predicted by first-principles theory will be discussed in connection to dynamics of plastic deformations and the structure of the shock wave front. In particular, the non-monotonic dependence of shear stresses on uniaxial compression might result in a significant delay or even freezing of the plastic response that was recently observed in MD simulations of strong shock waves in covalent solids. [Preview Abstract] |
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