Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session J30: Focus Session: High Pressure II: Equations of State |
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Sponsoring Units: DCOMP GSCCM Chair: Ramon Ravelo, University of Texas at El Paso Room: D139 |
Tuesday, March 16, 2010 11:15AM - 11:27AM |
J30.00001: Alloying and Pressure Effects on Material Strength from First Principles Lin H. Yang, Hyunchae Cynn, Jae-hyun Klepeis, John Pask, Robert Rudd, Michael Shaughnessy It is well known that impurities and alloying can have a profound influence on the strength properties of a material. For example, alloying tantalum (Ta) with 10\% tungsten (W) increases the yield strength of the material by more than a factor of two [1]. In this work, we have developed a predictive theory of alloying and pressure effects on material strength from first principles. To be specific, we use $Ta_{1-x}-W_{x}$ alloy as a prototype system where the generalized stacking fault energies and elastic moduli were calculated from first principles. These results were then used to access the pressure and alloying effects on the relative strength of $Ta_{1-x}-W_{x}$ alloys. Our results appear to be consistent with the general trend that the alloying effects can have profound impacts on the material strength. With the applied pressure up to 2Mbar, the alloying effects on the strength remain to be very profound. [Preview Abstract] |
Tuesday, March 16, 2010 11:27AM - 11:39AM |
J30.00002: Phase relations and hardness trends of ZrO$_{2}$ and HfO$_{2}$ at high pressure Yahya Al-Khatatbeh, Kanani Lee, Boris Kiefer We use high-resolution synchrotron x-ray powder diffraction and Density-Functional Theory to investigate the phase stability, equations of state (EOS), and mechanical hardness of ZrO$_{2}$ and HfO$_{2}$. For the equilibrium phase of ZrO$_{2}$ at ambient conditions (MI), we provide a new experimental 2$^{nd}$-order Birch-Murnaghan EOS that is comparable to results obtained from Brillouin measurements, but significantly different from previous high-pressure experiments: ambient-pressure bulk modulus $K_{0}$ of 210 ($\pm $28) GPa. For the high-pressure OI-ZrO$_{2}$ phase, we find that $K_{0}$ = 290 ($\pm $11) GPa which is 19-32{\%} higher than previously determined. The cotunnite OII phase is observed to be the most stable phase up to at least 54 and 100 GPa at room temperature after laser heating to $\sim $1800 ($\pm $200) K for ZrO$_{2}$ and HfO$_{2}$, respectively. The OI $\to $ OII phase transition in both ZrO$_{2}$ and HfO$_{2}$ yields a volume collapse of $\sim $10{\%}. Using scaling relations we obtain the hardness of OII-ZrO$_{2}$ of $\sim $10 GPa. As Hf and Zr have similar ionic radii, neither phase is likely to qualify as superhard. [Preview Abstract] |
Tuesday, March 16, 2010 11:39AM - 11:51AM |
J30.00003: ABSTRACT WITHDRAWN |
Tuesday, March 16, 2010 11:51AM - 12:27PM |
J30.00004: Equation of state research for ignition on NIF Invited Speaker: The design of Inertial Confinement Fusion (ICF) capsules for the National Ignition Campaign depends heavily on the use of models based on hydrodynamic simulations, which in turn require highly accurate equation of state (EOS) for the materials involved. In this talk, I will discuss our efforts to construct multiphase EOS and transport models for carbon at extreme pressures based on ab initio electronic structure calculations. In particular, the free energies of the solid phases are constructed from cold, ion-thermal and electron-thermal components determined from density functional based calculations and melting temperatures are computed with two-phase coexistence simulations. A simple solid-like free energy model is used to represent the liquid phase that is constrained by direct ab initio molecular dynamics simulations of the liquid phase as well as the computed melting temperatures of the different solid phases. By combining with a Thomas Fermi-based free energy model to represent the limits of extreme temperature and pressure a new multiphase EOS model has been constructed that is currently the basis for the high-density carbon ICF capsule design. A similar effort is underway to develop a multiphase table for beryllium as well. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Tuesday, March 16, 2010 12:27PM - 12:39PM |
J30.00005: High Pressure-Temperature Studies of Vanadium Zs. Jenei, B.J. Baer, H. Cynn, J-H. P. Klepeis, M.J. Lipp, W.J. Evans, H.-P. Liermann, S.V. Sinogeikin, W. Yang Vanadium, a seemingly simple metal, has captured the interest of high-pressure scientists following the discovery (Ding et al. PRL 2007) of a subtle pressure-induced phase transition from bcc to a rhombohedral phase. Recent first-principles electronic-structure studies (Lee et al. PRB 2008) are consistent with these experiments and extend beyond the range of the measurements, predicting a reentrant phase transition back to bcc at high pressure. We have made x-ray diffraction measurements of the crystal structure and lattice parameters of vanadium at high-pressure and temperature. Detailed comparisons will challenge/validate models and guide development of predictive codes. We will discuss our measurements including high temperature behavior, the EOS, and dependence of the transition pressure on the hydrostatic conditions of the compression/decompression. [Preview Abstract] |
Tuesday, March 16, 2010 12:39PM - 12:51PM |
J30.00006: Strength studies on V and Ta-W alloys using Diamond Anvil Cell Jae-Hyun Klepeis, Hyunchae Cynn, William Evans, Robert Rudd, Lin Yang, Hans-Peter Liermann, Wenge Yang The pressure-dependences of the quasi-static yield strength of polycrystalline forms of V and Ta-W alloys have been measured at room temperature using an implementation of a non-hydrostatic diamond anvil cell technique. A new feature of this work is the use of \textit{in situ} determination of the sample thickness and pressure with synchrotron X-ray. We adopt the conventional technique [C. Meade and R. Jeanloz, J. Geophys. Res. 93, 3261 (1988)] and the pointwise approach to determine the strength under Tresca yield criterion. The result shows the trend of the pointwise analysis is similar to the one of conventional approach. [Preview Abstract] |
Tuesday, March 16, 2010 12:51PM - 1:03PM |
J30.00007: First principles elasticity of olivine Maribel N\'u\~nezValdez, Renata Wentzcovitch, Koichiro Umemoto We examine by first principles the static elaticity of olivine, Mg$_{2-x}$Fe$_{x}$SiO$_{4}$ ($x = 0.125$), a major constituent of the Earth's upper mantle. We investigate the effect of atomic arrangement and composition on single crystal and poly-crystalline elastic moduli. Wave propagation anisotropy in single crystals and polarization anisotropy in aggregates with preferred orientation are also investigated and compared with those of forsterite for a thorough understanding of the effect of iron on these properties. [Preview Abstract] |
Tuesday, March 16, 2010 1:03PM - 1:15PM |
J30.00008: Effects of Impurities on the Optical Properties of Mixtures Dan Horner, Joel Kress, Lee Collins We perform molecular dynamics simulations\footnote{D.A, Horner et. al., Phys. Rev. B {\bf{80}}, 024305 (2009)} of mixtures of CH$_{2}$ and Aluminum (Al) in a plane-wave, finite-temperature density functional theory treatment at the generalized-gradient level with projector-augmented wave pseudopotentials for temperatures between 1eV and 3eV and densities ranging from 1 to 3 g/cm$^{3}$. In this regime, the system generally takes the form of an atomic liquid with the C, H, and Al all dissociated. We vary the concentration of Aluminum from 0\% to 100\% by substituting Al atoms for a CH$_2$ molecules in the initial configuration. Samples consisted of 75 CH$_2$ molecules [C=75; H=150] or their equivalent Al substitution although larger samples were introduced to test size effects. In general, the dc electrical conductivity varied smoothly with Al concentration with a slow increase up to 50\% and a steeper rise after about 70\%. The Rosseland Mean Opacities also behaved smoothly with a factor of two change between the extremes of the Al concentration. However, for a few combinations of density, temperature, and Al concentrations, we did find a ``condensation'' into a large polymer structure and noticeable changes in the system properties. [Preview Abstract] |
Tuesday, March 16, 2010 1:15PM - 1:27PM |
J30.00009: Multiphase Equation of State for Gallium Scott Crockett A recently developed multiphase equation of state for gallium will be used to illustrate the sensitivity of isentropic and shock compression results using different initial conditions. From ambient conditions, the equation of state predicts the unusual phenomenon of spontaneous spreading of a compression wave due to a sudden drop in the bulk modulus from the Ga I to liquid phase transition. The gallium multiphase equation of state has three solid phases and a liquid phase. We will also explore the effects of neglecting one of the solid phases, to simulate metastability. [Preview Abstract] |
Tuesday, March 16, 2010 1:27PM - 1:39PM |
J30.00010: Determination of the $\beta$--$\gamma$ pressure/temperature phase boundary for tin from dynamic isentropic compression experiments D.H. Dolan, J.L. Wise, J.-P. Davis, C.A. Hall, D.B. Hayes Electomagnetically driven stress-wave tests were conducted in Sandia's Dynamic Integrated Compression Experimental (DICE) Facility to measure the temperature dependence of the $\beta$--$\gamma$ solid/solid structural transition pressure in preheated tin samples subjected to ICE (Isentropic Compression Experiment) loading conditions. For several initial temperatures ranging from 20 to 200 C, velocity interferometer (VISAR) diagnostics provided time-resolved measurements of the sample free-surface motion. These measurements exhibited the distinct two-wave structure expected as a consequence of the phase transition. The locus of the $\beta$--$\gamma$ phase boundary was determined by iteratively adjusting the parameters in a multiphase material model for tin so as to optimize the aggregate agreement between one-dimensional wavecode simulations of the individual experiments with the actual ICE wave-profile data. [Preview Abstract] |
Tuesday, March 16, 2010 1:39PM - 1:51PM |
J30.00011: Molecular dynamics simulation of dynamic response of beryllium Aidan Thompson, Matthew Lane, Michael Desjarlais, Michael Baskes The response of beryllium to dynamic loading has been extensively studied, both experimentally and theoretically, due to its importance in several technological areas. Compared to other metals, it is quite challenging to accurately represent the various anomalous behaviors of beryllium using classical interatomic potentials. A new parameterization of the MEAM interatomic potential has been obtained, which reproduces ambient elastic and lattice constants, the melting temperature, and the static compression curve up to 200 GPa, and is free of obvious pathologies. Hugoniostat and direct molecular dynamics simulations using this parameterization, as well as one due to Dremov et al. have been used to predict the dynamic response of HCP beryllium up to and including melting. [Preview Abstract] |
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