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 Z7: CH.3 Chemistry: High Pressure Structures |
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Chair: Mario Santoro, Istituto di Fisica Applicata N. Carrara Room: Grand Crescent |
Friday, July 12, 2013 11:00AM - 11:30AM |
Z7.00001: Novel Molecular Alloys under Extreme Conditions Invited Speaker: Minseob Kim Novel van der Waals binary compounds, composed by two different molecular solids such as Xe and H2, H2 and O2, NH3 and H2, and CH4 and H2, are understood as ``molecular alloys'' in terms of a changing of coordination numbers or a formation of clathrate system which are comparable to the substitution or the occupation of atoms in the interstices of the host crystal lattice in metal alloy. Such molecular alloys show markedly differences in physical and chemical properties such as phase transitions, structural and electrical transition, optical changes, stiffness changes, and so on. In this presentation, three molecular alloys will be demonstrated. First, extended solid XeF2 which transforms to novel two- and three-dimensional extended non-molecular phases and their metalization arising from a pressure-induced delocalization of non-bonded lone-pair electrons of F. Second, N2-H2 system which shows the presence of a novel incommensurate-like (N2)12D2 system above 10 GPa and a non-crystalline $\delta$-N2-like non-crystalline solid that arises at the onset of solidification. Third, CO-D2 system which shows small amount of D2 stabilizes metastable polymeric CO at ambient conditions by forming O-D bonds which are playing a disproportionate effects on the non-bonded electron pairs of O. [Preview Abstract] |
Friday, July 12, 2013 11:30AM - 12:00PM |
Z7.00002: Band Gap of Materials from Refractive Indices at High Pressure Invited Speaker: John Tse The band gap of a material is one of the most fundamental properties. One approach to obtain energy gap information at high pressure is to measure the reflectivity of the material in a diamond anvil cell and analyzed with the effective oscillator model (EOM). In this study, the assumptions underlying the EOM are examined through comparison with theoretical dielectric response functions obtained from solving the Bethe-Salpeter equation (BSE) and band gap energy calculated from the GW method. The validity the EOM method in the estimation of the band gap energies from refractive index data in high pressure ice VII and solid hydrogen is evaluated. The research was performed in collaboration with Y. Liang, H. Shi, W. Yim, C.S. Zha and R.J. Hemley. [Preview Abstract] |
Friday, July 12, 2013 12:00PM - 12:15PM |
Z7.00003: Extreme Chemistry of Warm Dense Nitrogen Marius Millot, J. Ryan Rygg, Jon H. Eggert, Peter M. Celliers, Gilbert W. Collins, Raymond Jeanloz Nitrogen is a prototypical molecular system with a uniquely stable triple covalent bond. We conducted laser compression experiments of dense fluid nitrogen and obtained pressure-density-temperature Hugoniot data along with optical reflectivity in the warm dense regime up to 8 Mbar. Our data suggest that Nitrogen transforms to a polymeric conducting fluid around 8000 K and 1 Mbar that progressively dissociates into an atomic dense plasma at higher pressure and temperature. [Preview Abstract] |
Friday, July 12, 2013 12:15PM - 12:30PM |
Z7.00004: Modeling of amorphous poly-CO structure with N and He Iskander G. Batyrev, William D. Mattson Density functional theory simulations of amorphous poly-CO structure were performed with addition of N or He atoms to crystalline delta phase of CO. For the CO-N mixtures the concentration of N was varied in the range from 6.25{\%} to 50{\%} with different distribution of N atoms in the unit cell. For all studied concentrations and initial configurations, isotropic compression led to polymerization beginning at a pressure of 11 GPa. This is slightly higher than that for pure p-CO which was previously observed to start to polymerize at 8 GPa. For the nitrogen doped mixtures only the CO part of the mixtures polymerized at 11 GPa, and the N was not incorporated into the random network. For the CO-He mixtures, the concentration of He atoms in delta phase of CO was 6.25{\%}. Formation of random networks begins at 9 GPa and at 11 GPa all CO molecules have formed a combination of closed rings and chain type structures without isolated CO molecules with a density of 2.40 g/cm3. He atoms facilitate complete formation of the random structure at lower pressure than that for pure poly-CO, which isn't completely polymerized until compressed to a pressure of 18 GPa. He atoms also help stabilize the structure while lowering the pressure down to 100 Bar with only few CO molecules detaching in the process. Without He atoms at the same pressure there are approximately ten times the number CO molecules occupying voids in the random network. [Preview Abstract] |
Friday, July 12, 2013 12:30PM - 12:45PM |
Z7.00005: Ammonia ice at very high pressure Sandra Ninet, Frederic Datchi, Paul Dumas, Mohamed Mezouar, Gaston Garbarino, Adrien Mafety, Chris Pickard, Richard Needs, Marco Saitta In this presentation, we report an extended experimental investigation of the phase diagram of ammonia at high pressure and temperature. By combining Raman scattering and X-ray diffraction experiments, we demonstrate the presence of a new H-disordered crystalline form above $\sim$60 GPa and $\sim$700 K. Using \textit{ab initio} MD simulations, we show that this new disordered phase is a superionic conductor. We will also present new experimental results (infrared, Raman and X-ray) on NH$_{3}$ and ND$_{3}$ at ambient temperature up to 200 GPa and will discuss the existence of ionic ammonia ices. [Preview Abstract] |
Friday, July 12, 2013 12:45PM - 1:00PM |
Z7.00006: The structure of ice VII on the approach to symmetrisation Malcolm Guthrie, Reinhard Boehler, Christopher Tulk, Antonio Moreira dos Santos, Kuo Li, Jamie Molaison, Russell Hemley The symmetrisation of the H-bonds in water was first predicted almost 60 years ago [1]. In subsequent decades, the formation of symmetric ice X has been extensively studied. Neutron-diffraction studies of D$_{2}$O ice [2,3] are particularly useful in characterising the structure, providing the only direct measurements of the proton (deuteron) density distribution. However, to date, a limited maximum pressure (of \textless 30 GPa) for these studies has confined them to a regime where the water molecule geometry remains essentially unchanged from ambient pressure [3]. We will present an implementation of diamond-anvil-cell techniques for neutron powder diffraction at the SNS, Oak Ridge TN. This new capability permits neutron structural measurements up to at least 70 GPa. We will show data on crystalline D$_{2}$O up to these pressures, which approach those of the symmetrisation transition. \\[4pt] [1] B. Kamb {\&} B.L. Davis PNAS \textbf{52} 1433 (1964);\\[0pt] [2] W.F. Kuhs J. Chem. Phys. \textbf{81} 3612 (1984);\\[0pt] [3] R.J. Nelmes et al Phys. Rev. Lett. \textbf{81} 2719 (1998). [Preview Abstract] |
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