Hydrogen at high pressure

Maksimov, Evgenii G.; Shilov, Yu. I.

doi:10.1070/pu1999v042n11abeh000666

Cited by 51 publications

(31 citation statements)

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“…Metallization of solid molecular hydrogen has been reported in several experiments (Maksimov and Shilov, 1999), most recently in DAC experiments near 300 K and ∼ 265 GPa (Eremets and Troyan, 2011). However, opinions concerning the results have been mixed (Jephcoat, 2011;Nellis et al, 2012).…”

Section: The Metallization Of Solid Molecular Hydrogenmentioning

confidence: 92%

“…In a later section, we will discuss the shock experimental measurements of the conductivity of (Nellis et al, 1999;Weir et al, 1996), where the IM transition was observed at high temperature (∼ 2600 K) near 140 GPa in the liquid hydrogen phase. See also recent reviews (Maksimov and Shilov, 1999;Robitaille, 2011).…”

Section: The Metallization Of Solid Molecular Hydrogenmentioning

confidence: 99%

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The properties of hydrogen and helium under extreme conditions

McMahon¹,

Morales²,

Pierleoni³

et al. 2012

Rev. Mod. Phys.

478

415

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Hydrogen and helium are the most abundant elements in the universe and, in principle, are the simplest elements. Nonetheless, they display remarkable properties under pressure that have fascinated theoreticians and experimentalists for over a century. Recent advances in computational methods have made it possible to elucidate many of these properties. We review some of the computational methods that have been applied to dense hydrogen and helium in recent years, mainly those that perform a simulation directly from the physical picture of electrons and ions; primarily, those based on density functional theory and quantum Monte Carlo methods. We then discuss the predictions from such methods as applied to the phase diagram of hydrogen, including the solid and fluid phases, with particular focus on the crystal structures, the liquidliquid transition and comparison of the results with experimental shock-wave data. We then discuss predictions of ordered quantum states, including a possible low-temperature fluid and high-temperature superconductivity in the atomic state. We also briefly discuss pure helium, and then focus on hydrogen-helium mixtures, with particular focus on properties of relevance to planetary science.

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Section: The Metallization Of Solid Molecular Hydrogenmentioning

confidence: 92%

Section: The Metallization Of Solid Molecular Hydrogenmentioning

confidence: 99%

The properties of hydrogen and helium under extreme conditions

McMahon¹,

Morales²,

Pierleoni³

et al. 2012

Rev. Mod. Phys.

478

415

View full text Add to dashboard Cite

show abstract

“…1 shows a limited region of the phase diagram representative of dense hydrogen inferred from considerable experimental and theoretical effort (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17). Many of the structural characteristics of dense hydrogen are summarized in recent reviews (14,15) that augment the earlier review by Silvera (18). The transition (for T ϳ 0) at Ϸ150 GPa for both hydrogen and deuterium is notable, for it corresponds to an increase in proton-pair polarization that is about an order of magnitude greater than the phase II value (16).…”

Section: [4]mentioning

confidence: 99%

Order in dense hydrogen at low temperatures

Edwards

Ashcroft²

2004

Proc. Natl. Acad. Sci. U.S.A.

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By increase in density, impelled by pressure, the electronic energy bands in dense hydrogen attain significant widths. Nevertheless, arguments can be advanced suggesting that a physically consistent description of the general consequences of this electronic structure can still be constructed from interacting but state-dependent multipoles. These reflect, in fact self-consistently, a disorder-induced localization of electron states partially manifesting the effects of proton dynamics; they retain very considerable spatial inhomogeneity (as they certainly do in the molecular limit). This description, which is valid provided that an overall energy gap has not closed, leads at a mean-field level to the expected quadrupolar coupling, but also for certain structures to the eventual emergence of dipolar terms and their coupling when a state of broken charge symmetry is developed. A simple Hamiltonian incorporating these basic features then leads to a high-density, low-temperature phase diagram that appears to be in substantial agreement with experiment. In particular, it accounts for the fact that whereas the phase I-II phase boundary has a significant isotope dependence, the phase II-III boundary has very little.A t low temperatures and ordinary pressure, crystalline hydrogen has a mean electronic density that exceeds the valence electron density of all the alkali metals and even the alkaline earths under equivalent conditions. However, it is a ground state insulator retaining this physical characteristic at densities an entire order of magnitude higher than its one atmosphere value. Under these compressions application of band theory for rigorously static lattices shows clearly that the electronic energy bands of hydrogen are appreciably wide, indicating significant overlap between the standard orbitals invoked to describe the low density phases. Yet much of the electronic charge remains well localized in the vicinity of a Bohr radius from the protons, and there is evidence that the currently accessible part of the low temperature, high density phase diagram can still be understood in terms of interactions originating with multipole expansions associated with effectively localized states and a continuing preservation of the strongly inhomogeneous character of the microscopic electron density e (1) (r). The deeper understanding of this notion, and its consequences, constitutes the bulk of what follows, but starting from an elementary observation that a macroscopic neutral quantity of hydrogen is but a dual Fermion assembly of electrons and protons, and that the dynamics of the latter have considerable influence on the former. The Dense Hydrogen ProblemThe quantum mechanics of N(ϳ10 23 ) electrons in a uniform compensating charged continuum of volume V is a well studied problem, though debate still continues on the nature of its low density states (especially in reduced dimensionality). If v c (r) ϭ e 2 ͞r is the fundamental Coulomb interaction, and if e ϭ e(N͞V) is the corresponding rigid continuum charge density, the...

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“…From simple multi-electron consideration the metallic phase of NiO forms when the effective Hubbard energy, U eff , is almost equal to the estimated full bandwidth 2W. 2 A transition of an insulator into a metallic state is a general fundamental phenomenon related to a broad range of physical systems [1][2][3][4][5][6]. Nickel monoxide -NiO -is historically one of the first compounds, which was involved in the understanding of strongly correlated electronic systems.…”

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confidence: 99%

Insulator-Metal Transition in Highly Compressed NiO

2012

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The insulator-metal transition was observed experimentally in nickel monoxide NiO at very high pressures of ~240 GPa. The sample resistance becomes measurable at about 130 GPa and decreases substantially with the pressure increase to ~240 GPa. A sharp drop in resistance by about three orders of magnitude has been observed at ~240 GPa with a concomitant change of resistance type from semiconducting to metallic. This is the first experimental observation of an insulator-metal transition in NiO anticipated by Mott decades ago. From simple multi-electron consideration the metallic phase of NiO forms when the effective Hubbard energy, U eff , is almost equal to the estimated full bandwidth 2W. 2 A transition of an insulator into a metallic state is a general fundamental phenomenon related to a broad range of physical systems [1][2][3][4][5][6]. Nickel monoxide -NiO -is historically one of the first compounds, which was involved in the understanding of strongly correlated electronic systems. The importance of observing and understanding the insulator-metal transition in compressed NiO for condensed matter physics (correlated electron physics) ranks close to the metallization of hydrogen under pressure. Pioneering studies by Mott and co-workers treated NiO as a typical example of "Mott" insulator with a wide d-d energy gap U, which occurs due to strong Coulomb electron repulsion on the same Ni site [7][8][9][10] Here we report the observation of the insulator-metal transition in NiO. We find also that the lowest energy gap E g of the insulating phase under pressure can be rationalized based on the pressuredependent U, following simple predictions based on crystal field theory [22,23].Nickel monoxide is an antiferromagnetic insulator with a Néel point of 523 K at ambient pressure On the experimental side, the pressure of possible transition is expected to be above ~150 GPa. Here we describe in brief the experimental procedure of resistivity measurements. We have used thin NiO single crystal samples in a thin platelet shape, or samples compressed to a platelet shape from powder, with thickness about or less than 1 micron. The samples with lateral dimensions 15-30 microns were placed directly on the cBN surface of a preindented cBN gasket [30] (no pressure medium); four thin Pt foil leads (thinner than 1 micron) were placed on the surface of the sample and were clamped by the opposite anvil (see Fig. 1). The pressure was measured by the standard ruby technique in the range 0-100 GPa, and from the high energy edge of a first order Raman peak of diamond at higher pressures [31]. According to our estimates from pressure gradient along the culet[32], the uniaxial stress was about ± 10 GPa at the maximum pressures achieved in the experiments.The additional details of the resistivity experiments are described elsewere [31][32][33] and in supplementary information.We show the change in optical transparency of a NiO sample at the insulator-metal transition in Fig. 1. The sample is almost transparent at 35 GPa and is hardl...

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Hydrogen at high pressure

Cited by 51 publications

References 85 publications

The properties of hydrogen and helium under extreme conditions

The properties of hydrogen and helium under extreme conditions

Order in dense hydrogen at low temperatures

Insulator-Metal Transition in Highly Compressed NiO

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