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 Y2: CM.1 Equation of State: Hydrogen I |
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Chair: Rus Hemley, Carnegie Institution of Washington Room: Grand Ballroom II |
Friday, July 12, 2013 9:15AM - 9:45AM |
Y2.00001: LiH equation of state by static and shock compression Invited Speaker: Amy Lazicki We will present experimental progress towards a more complete picture of the equation of state of LiH at extreme conditions, for the purpose of constraining theoretical models. A high-precision 300K isotherm up to 2.5 Mbars was measured using X-ray diffraction on polycrystalline samples compressed in diamond anvil cells, revealing that LiH does not transform from the B1 phase to the predicted B2 phase in this pressure range. Raman spectroscopy probed the vibrational properties along the isotherm. We will also present new results from shock compression studies of the principle Hugoniot between 3 and 8 Mbars. Portions of this work were performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Friday, July 12, 2013 9:45AM - 10:00AM |
Y2.00002: Hydrogen in Simple Molecular Systems under Pressure Gustav Borstad, Choong-Shik Yoo Hydrogen-rich systems are studied due to their importance in revealing fundamental properties and giving rise to novel behaviors as well as the hope of using the currently known and remarkable properties of hydrogen for applications. The hydrogen molecule (and its isotopic forms) is of interest in its own right as the simplest molecule, yet it forms an extremely complicated solid with many interesting properties observed or expected to be observed under high pressure. Furthermore, the novel behavior observed in simple binary mixtures of hydrogen and simple molecular systems, such as water, ammonia, and methane, where the mixture alters the structure and properties of both systems, giving rise to a new system different from either specie alone. This provides interesting insights into the effects of the environment on these molecules and on their resulting interactions and properties. In this talk, we will present a summary of the results obtained from Raman spectroscopic studies on these systems, and we will compare and contrast the properties of these hydrogen-rich mixtures as the simple molecular species is varied. [Preview Abstract] |
Friday, July 12, 2013 10:00AM - 10:15AM |
Y2.00003: Unusual Stoichiometries of Hydrogen and Iodine Under Pressure Andrew Shamp, Eva Zurek Evolutionary structure searches are combined with density functional calculations to examine the most stable stoichiometries and structures of hydrogen rich iodine phases, H$_{\mathrm{n}}$I with n\textgreater 1, under pressure. With respect to decomposition into hydrogen and iodine the first of the stoichiometries, H$_{5}$I, is predicted to become thermodynamically preferred at $\sim$30 GPa and remain stable until H$_{2}$I, consisting of chains of molecular hydrogen within a iodine sublattice, becomes the global thermodynamic minimum at $\sim$90 Gpa. H$_{5}$I consisting of both molecular and atomic hydrogen within H---I---H chains is predicted to remain insulating until $\sim$70 GPa whereas the H$_{2}$I stoichiometry is predicted to become metallic at $\sim$5GPa, well before it becomes thermodynamically stable. A second metallic phase, H4I, present on the convex hull at pressures above 100 GPa is constructed of a graphene-like molecular hydrogen sublattice between layers of a hexagonal iodine sublattice. [Preview Abstract] |
Friday, July 12, 2013 10:15AM - 10:30AM |
Y2.00004: Isotopic Studies of Hydrogen and Deuterium Phase IV at Multi-Megabar Pressures Eugene Gregoryanz, Christophe Guillaume, Thomas Scheler, Ross Howie The recent discovery of the mixed atomic and molecular phase IV of hydrogen (deuterium) is exemplary of how the studies of hydrogen at multi-megabar pressures is constitutive to the understanding of simple systems at extreme compressions [1]. Through a series of high pressure Raman spectroscopic experiments we have conducted an isotopic comparison between hydrogen and deuterium in phase I. Isotopic studies not only reveal differences in phase stability, imposing constraints on the P-T phase diagram, but also provide strong evidence for structural phenomena, such as proton (deuteron) tunnelling [2,3]. New data will be presented over a wide temperature range. \\[4pt] [1] R.T. Howie, C.L Guillaume, T. Scheler, A.F. Goncharov and E. Gregoryanz, Phys. Rev. Lett., \textbf{108},125501 (2012).\\[0pt] [2] R.T. Howie, T. Scheler, C.L Guillaume, and E. Gregoryanz, Phys. Rev. B., \textbf{86}, 214104 (2012).\\[0pt] [3] A.F. Goncharov, J.S. Tse, H. Wang, J. Yang, V.V. Struzhkin R.T. Howie and E. Gregoryanz, Phys. Rev. B., \textbf{87}, 024101, (2013). [Preview Abstract] |
Friday, July 12, 2013 10:30AM - 10:45AM |
Y2.00005: Metallization of hydrogen and the essential differences between dynamic and static compression W.J. Nellis In 1935 Wigner and Huntington (WH) predicted that at density D$_{\mathrm{Thry}}=$0.62 mole H/cm$^{3}$, ``very low temperatures,'' and a pressure greater than 25 GPa, \textit{bcc} H$_{2}$ undergoes an isostructural phase transition directly to H with an associated insulator-metal transition (IMT). In 1996 metallic fluid H was made under dynamic compression in a cross over from H$_{2}$ to H that completes at D$_{\mathrm{exp}}=$0.64 mole H/cm$^{3}$, 140 GPa and T $\sim$ 2600 K. The Free-electron Fermi temperature T$_{\mathrm{F}}=$220,000 K and T/T$_{\mathrm{F}}=$0.012\textless \textless 1, as for ordinary metals at 300 K. To date solid metallic hydrogen has yet to be made at static pressures up to $\sim$360 GPa at T $\sim$ 300 K. This difference between electrical conductivity of H$_{2}$ compressed dynamically and statistically begs the question of why fluid H at 140 GPa and $\sim$3000 K becomes metallic at 0.64 mol H/cm$^{3}$, the density predicted by WH for their IMT at low T; whereas metallization of solid H$_{2}$ or H near 300 K is yet to be achieved experimentally at pressures up to $\sim$360 GPa? The answer is systematic differences induced by the rate of application of pressure in the two methods. Slow compression at $\sim$300 K strengthens solid H$_{2}$ by inducing intermolecular bonds, which impede dissociation, metallization and perhaps even thermal equilibrium. Fast dynamic compression of liquid H$_{2}$ up to $\sim$3000 K precludes formation of intermolecular H-H bonds, which permits fluid H$_{2}$ to weaken to dissociation and thus metallization at 140 GPa. Dynamic- and static-compression effects on materials will be compared in the context of how they effect metallization of hydrogen. [Preview Abstract] |
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