Metallic liquid hydrogen and likely Al2O3 metallic glass

Dynamic compression has been used to synthesize liquid metallic hydrogen at 140 GPa (1.4 million bar) and experimental data and theory predict Al2O3 might be a metallic glass at ~300 GPa. The mechanism of metallization in both cases is probably a Mott-like transition. The strength of sapphire causes shock dissipation to be split differently in the strong solid and soft fluid. Once the 4.5-eV H-H and Al-O bonds are broken at sufficiently high pressures in liquid H2 and in sapphire (single-crystal Al2O3), electrons are delocalized, which leads to formation of energy bands in fluid H and probably in amorphous Al2O3. The high strength of sapphire causes shock dissipation to be absorbed primarily in entropy up to ~400 GPa, which also causes the 300-K isotherm and Hugoniot to be virtually coincident in this pressure range. Above ~400 GPa shock dissipation must go primarily into temperature, which is observed experimentally as a rapid increase in shock pressure above ~400 GPa. The metallization of glassy Al2O3, if verified, is expected to be general in strong oxide insulators. Implications for Super Earths are discussed.Comment: 8 pages, 5 figures, 14th Liquid and Amorphous Metals Conference, Rome 201

The Structure of Jupiter, Saturn, and Exoplanets: Key Questions for High-Pressure Experiments

We give an overview of our current understanding of the structure of gas giant planets, from Jupiter and Saturn to extrasolar giant planets. We focus on addressing what high-pressure laboratory experiments on hydrogen and helium can help to elucidate about the structure of these planets.Comment: Invited contribution to proceedings of High Energy Density Laboratory Astrophysics, 6. Accepted to Astrophysics & Space Science. 12 page

Lattice Dynamics and the High Pressure Equation of State of Au

Elastic constants and zone-boundary phonon frequencies of gold are calculated by total energy electronic structure methods to twofold compression. A generalized force constant model is used to interpolate throughout the Brillouin zone and evaluate moments of the phonon distribution. The moments are used to calculate the volume dependence of the Gruneisen parameter in the fcc solid. Using these results with ultrasonic and shock data, we formulate the complete free energy for solid Au. This free energy is given as a set of closed form expressions, which are valid to compressions of at least V/V_0 = 0.65 and temperatures up to melting. Beyond this density, the Hugoniot enters the solid-liquid mixed phase region. Effects of shock melting on the Hugoniot are discussed within an approximate model. We compare with proposed standards for the equation of state to pressures of ~200 GPa. Our result for the room temperature isotherm is in very good agreement with an earlier standard of Heinz and Jeanloz.Comment: 13 pages, 8 figures. Accepted by Phys. Rev.

Interatomic potentials for atomistic simulations of the Ti-Al system

Semi-empirical interatomic potentials have been developed for Al, alpha-Ti, and gamma-TiAl within the embedded atomic method (EAM) by fitting to a large database of experimental as well as ab-initio data. The ab-initio calculations were performed by the linear augmented plane wave (LAPW) method within the density functional theory to obtain the equations of state for a number of crystal structures of the Ti-Al system. Some of the calculated LAPW energies were used for fitting the potentials while others for examining their quality. The potentials correctly predict the equilibrium crystal structures of the phases and accurately reproduce their basic lattice properties. The potentials are applied to calculate the energies of point defects, surfaces, planar faults in the equilibrium structures. Unlike earlier EAM potentials for the Ti-Al system, the proposed potentials provide reasonable description of the lattice thermal expansion, demonstrating their usefulness in the molecular dynamics or Monte Carlo studies at high temperatures. The energy along the tetragonal deformation path (Bain transformation) in gamma-TiAl calculated with the EAM potential is in a fairly good agreement with LAPW calculations. Equilibrium point defect concentrations in gamma-TiAl are studied using the EAM potential. It is found that antisite defects strongly dominate over vacancies at all compositions around stoichiometry, indicating that gamm-TiAl is an antisite disorder compound in agreement with experimental data.Comment: 46 pages, 6 figures (Physical Review B, in press

Thermodynamic model of hardness: Particular case of boron-rich solids

A number of successful theoretical models of hardness have been developed recently. A thermodynamic model of hardness, which supposes the intrinsic character of correlation between hardness and thermodynamic properties of solids, allows one to predict hardness of known or even hypothetical solids from the data on Gibbs energy of atomization of the elements, which implicitly determine the energy density per chemical bonding. The only structural data needed is the coordination number of the atoms in a lattice. Using this approach, the hardness of known and hypothetical polymorphs of pure boron and a number of boron-rich solids has been calculated. The thermodynamic interpretation of the bonding energy allows one to predict the hardness as a function of thermodynamic parameters. In particular, the excellent agreement between experimental and calculated values has been observed not only for the room- temperature values of the Vickers hardness of stoichiometric compounds, but also for its temperature and concentration dependencies

Saturn Atmospheric Structure and Dynamics

2 Saturn inhabits a dynamical regime of rapidly rotating, internally heated atmospheres similar to Jupiter. Zonal winds have remained fairly steady since the time of Voyager except in the equatorial zone and slightly stronger winds occur at deeper levels. Eddies supply energy to the jets at a rate somewhat less than on Jupiter and mix potential vorticity near westward jets. Convective clouds exist preferentially in cyclonic shear regions as on Jupiter but also near jets, including major outbreaks near 35°S associated with Saturn electrostatic discharges, and in sporadic giant equatorial storms perhaps generated from frequent events at depth. The implied meridional circulation at and below the visible cloud tops consists of upwelling (downwelling) at cyclonic (anti-cyclonic) shear latitudes. Thermal winds decay upward above the clouds, implying a reversal of the circulation there. Warm-core vortices with associated cyclonic circulations exist at both poles, including surrounding thick high clouds at the south pole. Disequilibrium gas concentrations in the tropical upper troposphere imply rising motion there. The radiative-convective boundary and tropopause occur at higher pressure in the southern (summer) hemisphere due to greater penetration of solar heating there. A temperature “knee ” of warm air below the tropopause, perhaps due to haze heating, is stronger in the summer hemisphere as well. Saturn’s south polar stratosphere is warmer than predicted by radiative models and enhanced in ethane, suggesting subsidence-driven adiabatic warming there. Recent modeling advances suggest that shallow weather laye

Nitrogen at very high pressure

High-pressure results for nitrogen are reviewed and discussed in terms of phenomena that occur at extreme conditions

Dense quantum hydrogen

Ultracondensed fluid metallic hydrogen has been made at high pressures. Solid metallic H would have several scientific and technological applications if metallic fluid hydrogen made at high pressures could be quenched metastably to a solid at ambient. The quantum nature of dense hydrogen is an issue both at high pressures and in materials recovered metastably on release of pressure. Quantum zero point vibrations of H might have a significant affect on properties of metallic H at high pressures and might adversely affect lifetimes of metastable solid hydrogen, which is particularly relevant for applications. Metallic (degenerate) fluid H has been made at finite temperatures with a reverberating shock wave under dynamic compressions and under static compressions in laser-heated diamond-anvil cells. The pressure-temperature (P–T) regime in those experiments ranged up to 180 GPa and 3000 K, in which metallic fluid H is a quantum-degenerate fluid with T/TF << 1, where TF is Fermi temperature. The lifetime of an experiment under static compression near 500 GPa at 5.5 K ranged up to weeks, sufficiently long to warrant concern about quantum diffusion having a major affect on the chemical composition of that metallic sample.Ультраконденсований рідкий металевий водень отримано при високому тиску. Металевий водень мав би багато наукових та технологічних застосувань, якби міг залишатися в метастабільному стані при нормальних умовах. Питання про квантову природу щільного водню актуальне як при високому тиску, так і для матеріалів, які залишаються метастабільними при скиданні тиску. Квантові нульові коливання можуть істотно впливати на властивості металевого H при високому тиску і можуть несприятливо позначатися на часи життя метастабільного твердого водню, що особливо актуально для практичних застосувань. Металева (вироджена) рідина H була отримана при динамічному та статичному стисненні в умовах зворотної ударної хвилі в алмазній ковадлі, що нагрівається лазером.Тиск та температура в цих експериментах становили до 180 ГПа та 3000 К, при яких металева рідина Н являє собою квантово-вироджену рідину з Т/ТF << 1, де TF — температура Фермі. Час проведення експерименту при статичному стисненні близько 500 ГПа й температурі 5,5 К становив до декількох тижнів, що достатньо для спостереження квантової дифузії, яка має істотний вплив на хімічний склад цього металевого зразка.Ультраконденсированный жидкий металлический водород получен при высоких давлениях. Металлический водород имел бы много научных и технологических применений, если бы мог оставаться в метастабильном состоянии при нормальных условиях. Вопрос о квантовой природе плотного водорода актуален как при высоких давлениях, так и для материалов, которые остаются метастабильными при сбросе давления. Квантовые нулевые колебания могут существенно влиять на свойства металлического H при высоких давлениях и могут неблагоприятно сказываться на временах жизни метастабильного твердого водорода, что особенно актуально для практических применений. Металлическая (вырожденная) жидкость H получена при динамическом и статическом сжатиях в условиях возвратной ударной волны в нагреваемой лазером алмазной наковальне. Давление и температура в этих экспериментах составляли до 180 ГПа и 3000 К, при которых металлическая жидкость Н представляет собой квантово-вырожденную жидкость с Т/ТF << 1, где TF — температура Ферми. Время проведения эксперимента при статическом сжатии около 500 ГПа и температуре 5,5 К составляло до нескольких недель, что достаточно для наблюдения квантовой диффузии, имеющей существенное влияние на химический состав этого металлического образца