Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Q30: Focus Session: High Pressure III |
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Sponsoring Units: DCOMP Chair: Ken Esler, University of Illinois at Urbana-Champaign Room: D139 |
Wednesday, March 17, 2010 11:15AM - 11:27AM |
Q30.00001: High Pressure Structure and Electrical Resistance Measurements on Cadmium Sulfide Nanoparticles J.M. Montgomery, A.K. Stemshorn, A. Stanishevsky, Y.K. Vohra, S.T. Weir Room-temperature four-probe electrical resistance and synchrotron x-ray diffraction measurements have been performed on dried and aqueous suspensions of CdS nanoparticles (25 nm in diameter) to 35 GPa. Nanoparticles used in these experiments were synthesized using the reaction between a cadmium salt and thiourea under hydrothermal conditions without using any surfactants. While the x-ray structure data confirms the irreversible wurtzite $\to $ rocksalt transition seen at 2.5 GPa in bulk CdS, the corresponding resistance drop was not observed in the measured range, indicating that the nanoparticle boundaries may prevent electronic communication between particles. Further studies on dry and aqueous 10 nm nano-spheres and 9 nm diameter nano-rods are planned, and the results of these experiments will be presented. [Preview Abstract] |
Wednesday, March 17, 2010 11:27AM - 11:39AM |
Q30.00002: Pressure-tuning of the thermal conductivity of a layered crystal, muscovite Wen-Pin Hsieh, Bin Chen, Jie Li, Pawel Keblinski, David Cahill We study the physics of heat conduction in layered, anisotropic crystals by measuring the cross-plane elastic constant $C_{33}$ and thermal conductivity $\Lambda $ of muscovite mica as a function of hydrostatic pressure. Picosecond interferometry and time-domain thermoreflectance provide high precision measurements of $C_{33}$ and $\Lambda $, respectively, of micron-sized samples within a diamond anvil cell; $\Lambda $ changes from the anomalously low value of 0.46 W m$^{-1}$ K$^{-1}$ at ambient pressure to a value more typical of oxides crystals with large unit cells, 6.6 W m$^{-1}$ K$^{-1}$, at $P$=24 GPa. We find good agreement between the data and a simple theoretical model that takes into account the pressure dependence of the cross-plane sound velocities. [Preview Abstract] |
Wednesday, March 17, 2010 11:39AM - 11:51AM |
Q30.00003: Electrical conductivity of Helium-Hydrogen mixtures Sebastien Hamel, Miguel Morales, Eric Schwegler Mixtures of helium and hydrogen at high pressures and temperatures are major components of jovian planets. The pressures and temperatures in their deep interiors can reach several Mbar and several 1000 K, conditions corresponding to the fluid metallic phase. Using quantum molecular dynamics, we explore the properties of these mixtures at planetary conditions. In particular we discuss the electrical conductivity at high pressure and high temperature of those mixtures in comparison to pure hydrogen. Prepared by LLNL under Contract DE-AC52-07NA27344. [Preview Abstract] |
Wednesday, March 17, 2010 11:51AM - 12:03PM |
Q30.00004: ABSTRACT WITHDRAWN |
Wednesday, March 17, 2010 12:03PM - 12:15PM |
Q30.00005: Pressure-induced volume collapse in PbCrO$_{3 }$-- a combined experimental and theoretical investigation P. Ganesh, R.E. Cohen, Wensheng Xiao, Ho-kwang Mao PbCrO$_{3}$ in perovskite structure surprisingly has a larger volume (a $\sim $ 4.0 {\AA} ) [1, 2] compared to PbTiO$_{3 }$(a $\sim $ 3.95 {\AA}). We synthesized a powder sample of PbCrO$_{3}$ and performed x-ray diffraction studies in a diamond anvil cell up to $\sim $ 30GPa. Our experiments show a pressure induced volume collapse at 1.6GPa by $\sim $9.8{\%}. To investigate its origin we performed DFT computations with LDA+U and GGA+U using ABINIT, relaxing the strain and the internal coordinates, for different distorted perovskite phases and spin configurations. We identified the volume collapse with the high pressure phase being cubic and the low-pressure phase being tetragonal and non-centrosymmetric. The spin-configuration is G-AFM with a local moment of $\sim $ 2.2$\mu _{B}$, comparable to experiments [1]. No spin or metal-insulator transition is observed in our computations. Rather, orbital ordering stabilizes the low pressure phase. Computations show the bulk moduli of the two phases to be very different, consistent with our experiments. Both phases are metallic. [1] W. L. Roth \textit{et.al}., J. Appl. Phys. \textbf{38}, 951 (1967), [2] Angel M. Arivalo-Lopez \textit{et.al}., J. Solid State Chemistry \textbf{180}, 3271 (2007) [Preview Abstract] |
Wednesday, March 17, 2010 12:15PM - 12:27PM |
Q30.00006: Abnormal high-pressure structural transitions; the curious case of GaFeO$_{3}$ Moshe Paz-Pasternak, R. Arielly, W.M. Xu, G.M. Rozenberg, R. Jeanloz, R.D. Taylor High pressure studies have been carried out in the antiferromagnetic-insulator GaFeO$_{3}$ (SG\textit{ Pc2}$_{1}n) $to 90 GPa using XRD at RT, Moessbauer spectroscopy, [MS(P,T)], and resistance measurements [R(P,T)]. Both MS(P,T) and R(P,T) studies reveal a \textit{Mott-Hubbard} correlation breakdown, starting at 50 GPa and culminating at 65 GPa, manifested by loss of paramagnetism concurring with a insulator-metal transition. XRD studies reveal a sluggish 1$^{st}$-order phase transition in the 25 -- 38 GPa range characterized by a discontinuous volume change ( 5{\%}) and formation of a perovskite structure (\textit{Pc2}$_{1}n \quad >$ \textit{Pbnm}). At $\sim $50 GPa an isostructural transition with 3.5{\%} volume decrease is observed, consistent with the MS and R(P,T) findings. At decompression the EOS follows a non-hysteretic curve down to 24 GPa, below which a 1$^{st}$-order transition occurs forming an ilmenite state (\textit{Pbnm$>$R3}), with a slight increase in V ($\sim $1{\%}), stable down to ambient pressure. The perovskite stability beyond 25 GPa and the peculiar \textbf{perovskite -ilmenite} will be discussed. [Preview Abstract] |
Wednesday, March 17, 2010 12:27PM - 12:39PM |
Q30.00007: Pressure dependence of exchange interactions and Neel temperature in transition metal oxides Julius Ojwang, Ronald Cohen, Luke Shulenburger, Xiangang Wan, Serjey Savrasov We perform first-principles linear response computations within LDA+U and GGA+U to systematically investigate the pressure dependence of magnetic exchange interactions for archetypal transition metal oxides (TMOs): MnO, FeO, CoO, and NiO. We obtain the Neel temperatures (T$_N$) using Monte Carlo simulations. We find that the magnitude of the next nearest neighbor coupling constant, J2, which dominates T$_N$, increases with increasing pressure, while the nearest neighbor, J1, behaves differently for the four TMOs. The variation of T$_N$ with pressure is influenced by interplay between the nearest and next nearest neighbor exchange coupling constants. Our results are found to be in agreement in general with most experiments [1-3]. \\[4pt] [1] Massey et al. Phys. Rev. B 42:8776, 1990\\[0pt] [2] Sidorov Appl. Phys. Lett. 72:2174, 1998\\[0pt] [3] Badro et al. Phys. Rev. Lett. 83:4101, 1999\\[0pt] [4] Pasternak et al. Phys. Rev. Lett. 79:5046, 1997 [Preview Abstract] |
Wednesday, March 17, 2010 12:39PM - 12:51PM |
Q30.00008: Spin states and hyperfine interactions of iron in (Mg,Fe)SiO$_{3}$ perovskite under pressure Peter Blaha, Han Hsu, Koichiro Umemoto, Renata Wentzcovitch We have found several metastable equilibrium sites for substitutional iron in (Mg,Fe)SiO$_{3}$ with the guidance of first-principles phonon calculations. In the relevant energy range, there are two distinct sites for high-spin (HS), one for low-spin (LS), and one for intermediate-spin (IS) iron. The two competing HS sites have different iron nucleus quadrupole splittings (QS) due to their different $d$-orbital occupancies. At low pressure, the HS site with QS of 2.3 mm/s is more stable, while the HS site with QS of 3.3 mm/s is more favorable at higher pressure. The crossover from low-QS to high-QS site occurs between 4 and 24 GPa, depending on the exchange-correlation functional and on the inclusion of Hubbard $U$. Our calculation supports the notion that the transition observed in recent M\"ossbauer spectra corresponds to an atomic site change rather than a spin-state crossover. [Preview Abstract] |
Wednesday, March 17, 2010 12:51PM - 1:03PM |
Q30.00009: X-ray emission spectroscopy of cerium under pressure across the volume collapse transition Magnus Lipp, Brian Maddox, Hyunchae Cynn, William Evans, Paul Chow, Yuming Xiao The satellite structure of the L$\gamma _{1}$ emission line of elemental cerium generated by the exchange interaction of the 4$f $with the 4$d$ level and thus indicative of the 4$f$ moment has been studied by X-ray emission spectroscopy. The strength of the moment was measured by integrating the area under the satellite versus energy and comparing it with the very weak structure of the nominally tetravalent CeO$_{2}$ at ambient conditions. We find that cerium's 4$f$ moment reduces by approximately 35 {\%} across the $\gamma -\alpha $ phase volume collapse (VC). The moment remaining in the $\alpha $-phase does not change significantly up to 45 kbar. The data lend further support to the Kondo VC model since most of the 4f electrons remain strongly correlated across the transition. [Preview Abstract] |
Wednesday, March 17, 2010 1:03PM - 1:15PM |
Q30.00010: A photoacoustic technique to measure speeds of sound from high-pressure fluids and solids: On the detonation chemistry of boron Joseph M. Zaug, Sorin Bastea, Jonathan Crowhurst, Nick Teslich We predict detonation, propellant, and combustion chemistry using a thermochemical computational model derived from interatomic potentials constructed from shockwave, thermodynamic, and speeds of sound (SoS) data from highly compressed reaction product fluids and mixtures, e.g., H2O, CO2, NH3, simple hydrocarbons, etc. Typically we employ impulsive stimulated light scattering to measure SoS. Here we discuss how an acoustic wave can be launched from a thin platinum film by absorption of a focused 1064 nm laser pulse. (Platinum lines were deposited onto diamond anvil culets using a focused ion beam.) Light scattered from a time-delayed probe pulse is phase modulated by a traveling acoustic pulse and collected using a PMT. Fourier transformations of measured time-domain series yield the frequency of acoustic waves. We demonstrate the utility of this technique applied to metaboric acid (HBO2). Corresponding predictions of extreme condition boron chemistry are given on the basis of our HBO2 equation of state. [Preview Abstract] |
Wednesday, March 17, 2010 1:15PM - 1:27PM |
Q30.00011: ABSTRACT WITHDRAWN |
Wednesday, March 17, 2010 1:27PM - 1:39PM |
Q30.00012: Multiscale Simulation of Hot Spot Ignition Laurence Fried High explosive shock sensitivity is controlled by a combination of mechanical response, thermal properties, and chemical properties. How these properties interplay in realistic condensed energetic materials is not well understood. In this paper, we use a multiscale approach to achieve a realistic simulation of hot spot (void) ignition in a single crystal of the explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). The smallest length scale (< 10 nm) of the multiscale model was treated quantum mechanically. We have conducted multiple simulations of the decomposition of the explosive TATB using density functional tight binding molecular dynamics (DFTB-MD). Nanoscale continuum simulations were performed of void ignition using the ALE3D hydrodynamic/thermal/chemical code. The simulations were performed with mesh sizes as fine as 10 nm in 2 dimensions with axisymmetric symmetry. We find that thermal transport does not significantly change void shape during the compression phase before chemistry begins. On the other hand, temperatures are dramatically affected by thermal transport. [Preview Abstract] |
Wednesday, March 17, 2010 1:39PM - 1:51PM |
Q30.00013: Quantum Mechanical Corrections to Simulated Shock Hugoniot Temperatures Nir Goldman, Evan Reed, Laurence E. Fried We present a straightforward method for the inclusion of quantum nuclear vibrational effects in molecular dynamics calculations of shock Hugoniot temperatures. Using a Gr\"{u}neisen equation of state and a quasi-harmonic approximation to the vibrational energies, we derive a simple, post-processing method for calculation of the quantum corrected Hugoniot temperatures. We have used our novel technique on \textit{ab initio} simulations of both shock compressed water and methane. Our results indicate significantly closer agreement with all available experimental temperature data for these two systems. Our formalism and technique can be easily applied to a number of different shock compressed molecular liquids or solids, and has the potential to decrease the large uncertainties inherent in many experimental Hugoniot temperature measurements of these systems. [Preview Abstract] |
Wednesday, March 17, 2010 1:51PM - 2:03PM |
Q30.00014: A High-Temperature Diamond Anvil Cell Technique using Electrical Microheater Elements Samuel Weir, Damon Jackson, Steven Falabella, Gopi Samudrala, Yogesh Vohra A technique has been developed for heating high-pressure metal samples to very high temperatures by means of electrical resistive heating of thin-film heating elements in a diamond anvil cell. Key features of this design include the use of chemical vapor deposited (CVD) layers of diamond for electrical insulation, and thin-film lithographic patterning for fabrication of the heating elements. Data will be presented from a heating experiment on gold to 20 GPa and T=2000K. [Preview Abstract] |
Wednesday, March 17, 2010 2:03PM - 2:15PM |
Q30.00015: In-situ optical characterization in large volume presses using fibers and diamond anvil assembly Amartya Sengupta, Choong-Shik Yoo Recent advances in high-pressure technologies and in-situ laser spectroscopic and synchrotron x-ray probes lead to unprecedented opportunities of discovering new materials with advanced properties at extreme conditions. Yet, the use of such novel materials has been limited because of either a minute amount ($\sim $ng) of samples in DAC or the absence of in-situ optical characterization systems in large volume presses. Here, we report a unique optical window design based on (a) WC diamond anvil assembly and (b) sintered diamond (SD) diamond anvil assembly inside the PEC which allows optical access to the sample chamber for laser heating and Raman spectroscopy measurements. The optical signal recovery system is a hybrid design consisting of both fibers and free space optics for studying gravity related effects on crystal growth conditions. We have demonstrated the performance of the optical instrumentation and the diamond anvil assembly arrangement by in-situ Raman investigations of the phase transformations in Nitrogen and Carbon Dioxide upto 15 GPa. [Preview Abstract] |
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