Bulletin of the American Physical Society
18th Biennial Intl. Conference of the APS Topical Group on Shock Compression of Condensed Matter held in conjunction with the 24th Biennial Intl. Conference of the Intl. Association for the Advancement of High Pressure Science and Technology (AIRAPT)
Volume 58, Number 7
Sunday–Friday, July 7–12, 2013; Seattle, Washington
Session C2: CM.1 Equation of State: Oxides |
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Chair: Jason Scharff, Los Alamos National Laboratory Room: Grand Ballroom II |
Monday, July 8, 2013 11:00AM - 11:15AM |
C2.00001: Characterization of the release response of alpha-quartz in the multi-Mbar regime for use as an impedance match standard Marcus Knudson, Michael Desjarlias Alpha-quartz has been used prolifically in recent years as an impedance match standard in the multi-Mbar regime. This is due to the fact that above about 90 GPa quartz becomes reflective, and thus shock velocities can be measured to high precision using velocity interferometry. This property allows for high precision measurements, however, the accuracy of such measurements depends upon the knowledge of both the Hugoniot and the release or re-shock response of alpha-quartz. In previous work, we accurately determined the Hugoniot response of alpha-quartz through numerous plate-impact Hugoniot experiments on the Sandia Z machine. Here we present the results of several adiabatic release measurements of alpha-quartz over the range of 2-10 Mbar using 110 and 200 mg/cc silica aerogels, and full density polymethylpentene (commonly known as TPX). These data were used to determine a simple method to perform impedance matching calculations without the need to appeal to any tabular equation of state for quartz. The method also allows for propagation of all uncertainty, including the random measurement uncertainty and the uncertainty of the Hugoniot and release response of alpha-quartz. This model and several examples of its use will be discussed. [Preview Abstract] |
Monday, July 8, 2013 11:15AM - 11:30AM |
C2.00002: Hugoniot temperature measurements of Sapphire using laser-induced decaying shocks Takayoshi Sano, Norimasa Ozaki, Tomoaki Kimura, Kohei Miyanishi, Ryosuke Kodama, Taku Tsuchiya, Tatsuhiro Sakaiya, Keisuke Shigemori, Toshihiko Kadono, Yoichiro Hironaka, Masahiro Ikoma, Takuo Okuchi, Toshimori Sekine Properties of Sapphire at TPa regime are of great scientific interest. The EOS and conductivity of Sapphire at this condition are crucial to understand the interior structure of super-Earth exoplanets. Metallic transition of Sapphire is suggested to be similar to that of liquid Hydrogen (Mott-like transition). Then, we performed laser shock experiments on the Hugoniot measurements of Sapphire by GEKKO system at Osaka University. Taking advantage of decaying shock feature, Hugoniot temperature and optical reflectivity were measured in a wide range of the pressure. The reflectivity increases gradually from around 0.6 TPa and reaches 15\% at 1.3 TPa. The increase of the internal energy is observed at this regime, and the Hugoniot curve deviates from the isotherm. Obtained Hugoniot temperature shows little increase between 0.6 to 1 TPa. This trend cannot be seen in the SESAME EOS model and could be related to the dissociation of Sapphire. We focus on this transition process, and investigate it in detail with the help of ab initio molecular dynamics simulations. [Preview Abstract] |
Monday, July 8, 2013 11:30AM - 12:00PM |
C2.00003: The phase diagram and transport properties of MgO from theory and experiment Invited Speaker: Luke Shulenburger Planetary structure and the formation of terrestrial planets have received tremendous interest due to the discovery of so called super-earth exoplanets. MgO is a major constituent of Earth's mantle, the rocky cores of gas giants and is a likely component of the interiors of many of these exoplanets. The high pressure - high temperature behavior of MgO directly affects equation of state models for planetary structure and formation. In this work, we examine MgO under extreme conditions using experimental and theoretical methods to determine its phase diagram and transport properties. Using plate impact experiments on Sandia's Z facility the solid-solid phase transition from B1 to B2 is clearly determined. The melting transition, on the other hand, is subtle, involving little to no signal in us-up space. Theoretical work utilizing density functional theory (DFT) provides a complementary picture of the phase diagram. The solid-solid phase transition is identified through a series of quasi-harmonic phonon calculations and thermodynamic integration, while the melt boundary is found using phase coexistence calculations. One issue of particular import is the calculation of reflectivity along the Hugoniot and the influence of the ionic structure on the transport properties. Particular care is necessary because of the underestimation of the band gap and attendant overestimation of transport properties due to the use of semi-local density functional theory. We will explore the impact of this theoretical challenge and its potential solutions in this talk. The integrated use of DFT simulations and high-accuracy shock experiments together provide a comprehensive understanding of MgO under extreme conditions. [Preview Abstract] |
Monday, July 8, 2013 12:00PM - 12:15PM |
C2.00004: Ab-initio calculations of high pressure equation of state and ideal strength of MgO D. Mukherjee, K.D. Joshi, S.C. Gupta Isotherm at 0 K of fcc MgO is determined from ab-initio calculations and used to derive the 300 K isotherm, isentrope and Hugoniot of MgO. The shock parameters C and s obtained from theoretical Hugoniot are 6.74 km/s and 1.23 as compared to the experimental values of 6.87 km/s and 1.24, respectively. Further, we have determined ideal compressive strength and tensile strength of MgO single crystal subjected to uniaxial compressive and tensile loading along [001] direction under two deformation conditions, namely uniaxial strain condition and uniaxial stress condition. Examination of elastic stability conditions suggests that for [001] compressive loading, the MgO fails mechanically due to shear instability, whereas for expansion it fails due to vanishing of tensile modulus. The ideal compressive strength under uniaxial strain condition and uniaxial stress condition is determined to be 293 GPa and 123 GPa, respectively. However, ideal tensile strength$_{\mathrm{\thinspace }}$is evaluated to be -20 GPa and -11 GPa, respectively, for two loading conditions. Our results suggest that MgO single crystal offers higher resistance against failure for compression as well as expansion under uniaxial strain condition than that for the uniaxial stress condition. [Preview Abstract] |
Monday, July 8, 2013 12:15PM - 12:30PM |
C2.00005: A multiphase equation of state for cerium (IV) oxide Eric Chisolm I describe the construction of a theoretical equation of state (EOS) for cerium (IV) oxide, CeO$_{2}$, that includes a low- and high-pressure solid phase and the liquid. After quickly summarizing the standard models we use in each phase, I discuss challenges unique to the multiphase construction. I also describe some physical issues that appear in the Ce$_{x}$O$_{y}$ group of materials, including the possibility that CeO$_{2}$ changes chemical identity before melt. Finally, I briefly consider the challenge of comparing a full-density EOS to highly porous Hugoniot data. [Preview Abstract] |
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