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August 2015 - present
May 2013 - August 2015
Publications
Publications (79)
Various icy moons, such as Europa and Ganymede, have thin oxygen atmospheres and exhibit spectral features attributed to oxygen held in their surface ices. The oxygen forms from the radiolysis of water. The interiors of these bodies are subject to high pressures and it is not known how deep into icy moons oxygen-bearing ices can penetrate, or the s...
Carbon, nitrogen, and hydrogen are among the most abundant elements in the solar system, and our understanding of their interactions is fundamental to prebiotic chemistry. CH4 and N2 are the simplest archetypical molecules formed by these elements and are both markedly stable under extremes of pressure. Through a series of diamond anvil cell experi...
Carbon, nitrogen, and hydrogen are among the most abundant elements in the solar system, and our understanding of their interactions is fundamental to prebiotic chemistry. CH4 and N2 are the simplest archetypical molecules formed by these elements and are both markedly stable under extremes of pressure. Through a series of diamond anvil cell experi...
High-pressure synthesis of lutetium hydrides from molecular hydrogen (H2) and lutetium (Lu) is systematically investigated using synchrotron X-ray diffraction, Raman spectroscopy, and visual observations. We demonstrate that the reaction pathway between H2 and Lu invariably follows the sequence Lu ⟶ LuH2 ⟶ LuH3 and exhibits a notable time dependenc...
Under high pressure, methane and hydrogen form ( CH 4 ) 2 H 2 , CH 4 ( H 2 ) 2 , and ( CH 4 ) 3 ( H 2 ) 25 van der Waals compounds with stoichiometries determined by the H 2 concentration. This study investigates the effect of compression rates (up to 183 GPa/s) on the formation and morphology of these compounds at pressures up to 60 GPa utilizing...
The Na–W–H and Na–Re–H ternary systems were studied in a diamond anvil cell through X-ray diffraction and Raman spectroscopy, supported by density functional theory and molecular dynamics calculations. Na3WH9 can be synthesized above 7.8 GPa and 1400 K, remaining stable between at least 0.1 and 42.1 GPa. The rhenium analogue Na3ReH8 can form at 10....
Inorganic ternary metal–C–N compounds with covalently bonded C–N anions encompass important classes of solids such as cyanides and carbodiimides, well known at ambient conditions and composed of [CN]⁻ and [CN2]2– anions, as well as the high-pressure formed guanidinates featuring [CN3]5– anion. At still higher pressures, carbon is expected to be 4-f...
The reactivity between NaH and H2 has been investigated through a series of high-temperature experiments up to pressures of 78 GPa in diamond anvil cells combined with first principles calculations. Powder X-ray diffraction measurements show that heating NaH in an excess of H2 to temperatures around 2000 K above 27 GPa yields sodium trihydride (NaH...
Multilayer graphane (hydride of graphite) is a solid hydrocarbon of composition CH, which can be synthesized from graphite and molecular hydrogen at pressures above 2 GPa [V.E. Antonov
et al., Carbon 100 (2016) 465]. Using X-ray diffraction, this compound was preliminarily identified as the “graphane II” phase of 3D-graphane predicted by ab initio...
Using optical spectroscopy, X-ray diffraction, and electrical transport measurements, we have studied the pressure-induced metallization in BaH2 and Ba8H46. Our combined measurements suggest a structural phase transition from BaH2-II to BaH2-III accompanied by band gap closure and transformation to a metallic state at 57 GPa. The metallization is c...
The binary Xe–Ar system has been studied in a series of high pressure diamond anvil cell experiments up to 60 GPa at 300 K. In-situ x-ray powder diffraction and Raman spectroscopy indicate the formation of a van der Waals compound, XeAr2, at above 3.5 GPa. Powder x-ray diffraction analysis demonstrates that XeAr2 adopts a Laves MgZn2-type structure...
Through a series of high pressure diamond anvil experiments, we report the synthesis of alkaline earth (Ca, Sr, Ba) tetrahydrides, and investigate their properties through Raman spectroscopy, X-ray diffraction, and density functional theory calculations. The tetrahydrides incorporate both atomic and quasi-molecular hydrogen, and we find that the fr...
Through a series of x-ray diffraction, optical spectroscopy diamond anvil cell experiments, combined with density functional theory calculations, we explore the dense CH_{4}-H_{2} system. We find that pressures as low as 4.8 GPa can stabilize CH_{4}(H_{2})_{2} and (CH_{4})_{2}H_{2}, with the latter exhibiting extreme hardening of the intramolecular...
Diamond and graphite are fundamental sources of carbon in the upper mantle, and their reactivity with H 2 -rich fluids present at these depths may represent the key to unravelling deep abiotic hydrocarbon formation. We demonstrate an unexpected high reactivity between carbons’ most common allotropes, diamond and graphite, with hydrogen at condition...
Earth-abundant antimony trisulfide (Sb2S3), or simply antimonite, is a promising material for capturing natural energies like solar power and heat flux. The layered structure, held up by weak van-der Waals forces, induces anisotropic behaviors in carrier transportation and thermal expansion. Here, we used stress as mechanical stimuli to destabilize...
Hydrogen bond networks play a crucial role in biomolecules and molecular materials such as ices. How these networks react to pressure directs their properties at extreme conditions. We have studied one of the simplest hydrogen bond formers, hydrogen chloride, from crystallization to metallization, covering a pressure range of more than 2.5 million...
Hydrogen, the lightest element in the periodic table, has been predicted to metalize under extreme compression. Metallic hydrogen is believed to be a room-temperature superconductor. Due to the considerable experimental challenges of reaching such a state, the material has often been deemed the holy grail of condensed matter physics. It was then re...
Through a series of high-pressure x-ray diffraction experiments combined with in situ laser heating, we explore the pressure–temperature phase diagram of germanium (Ge) at pressures up to 110 GPa and temperatures exceeding 3000 K. In the pressure range of 64–90 GPa, we observe orthorhombic Ge-IV transforming above 1500 K to a previously unobserved...
We present a method for calculation of Raman modes of the quantum solid phase I hydrogen and deuterium. We use the mean-field assumption that the quantized excitations are localized on one molecule. This is done by explicit solution of the time-dependent Schroedinger equation in an angle-dependent potential, and direct calculation of the polarizati...
Raman spectroscopy demonstrates that the rotational spectrum of solid hydrogen, and its isotope deuterium, undergo profound transformations upon compression while still remaining in phase I. We show that these changes are associated with a loss of quantum character in the rotational modes, ie. with increasing pressure, the angular momentum J gradua...
The Co-H system has been investigated through high-pressure high-temperature x-ray diffraction experiments combined with first principles calculations. On compression of elemental cobalt in a hydrogen medium, we observe fcc cobalt hydride (CoH) and cobalt dihydride (CoH2) at 33 GPa. Laser heating CoH2 in a hydrogen matrix at 75 GPa to temperatures...
Significance
When hydrogen and deuterium are mixed, they form H 2 +HD + D 2 mixtures at very low pressures and room temperature. We show that at high pressures and low temperatures these mixtures behave as an isotopic molecular alloy (ideal solution); exhibiting symmetry-breaking phase transitions between phases I, II, and III; and shifting the tra...
By combining hydrogen and sulfur within diamond-anvil cells we synthesize (H2S)2H2 at 5 GPa and 373 K. Through a series of Raman spectroscopy, infrared spectroscopy, and synchrotron x-ray diffraction experiments we have constrained the phase diagram of (H2S)2H2 within a wide P−T range. On compression we observe the phase transition sequence of I-II...
The hydrogen molecule is made from the first and lightest element in the periodic table. When hydrogen gas is either compressed or cooled, it forms the simplest molecular solid. This solid exhibits many interesting and fundamental physical phenomena. It is believed that if the density of the solid is increased by compressing it to very high pressur...
We present a method for calculation of Raman modes of the quantum solid phase I solid hydrogen and deuterium. We use the mean-field assumption that the quantised excitations are localized on one molecule. This is done by explicit solution of the time-dependent Schroedinger equation in an angle-dependent potential, and direct calculation of the pola...
When compressed in a matrix of solid hydrogen, many metals form compounds with increasingly high hydrogen contents. At high density, hydrogenic sublattices can emerge, which may act as low-dimensional analogues of atomic hydrogen. We show that at high pressures and temperatures, ruthenium forms polyhydride species that exhibit intriguing hydrogen s...
Rare earth element polyhydrides have been predicted to exhibit high-Tc superconductivity at extreme compressions. Through a series of in situ high-pressure high-temperature x-ray powder diffraction experiments combined with density functional theory calculations, we report the emergence of polyhydride species in the praseodymium-hydrogen system. We...
Through a series of x-ray diffraction experiments, combined with first-principles calculations, we show that the nobility of platinum can be overcome, reacting with lithium under compression at room temperature. Pressures as low as 2.3 GPa lead to the synthesis of Li11Pt2, exhibiting the highest lithium content of any known intermetallic compound....
DOI:https://doi.org/10.1103/PhysRevLett.122.199602
The original version of this Article omitted references to previous experimental reports on solid hydrogen that are relevant for a full understanding of the context of the previous work. The added references are: 47. Akahama, Y. et al. Evidence from x-ray diffraction of orientational ordering in phase III of solid hydrogen at pressures up to 183 GP...
Hydrogen chemistry at extreme pressures is currently subject to extensive research due to the observed and predicted enhanced physical properties when hydrogen is incorporated in numerous binary systems. Despite the high reactivity of hydrogen, the noble metals (Cu, Ag, and Au) display an outstanding resilience to hydride formation, with no reports...
Diatomic elemental solids are highly compressible due to the weak interactions between molecules. However, as the density increases the intra- and intermolecular distances become comparable, leading to a range of phenomena, such as structural transformation, molecular dissociation, amorphization, and metallisation. Here we report, following the cry...
Transition metal nitrides have applications in a range of technological fields. Recent experiments have shown that new nitrogen-bearing compounds can be accessed through a combination of high temperatures and pressures, revealing a richer chemistry than was previously assumed. Here, we show that at pressures above 50 GPa and temperatures greater th...
The Raman spectra of liquid H 2 (D 2) have been collected in diamond anvil cell as a function of temperature at 3 GPa covering the range from 80 to ∼ 1000 K. Temperatures were measured using two independent methods: by thermocouple and from the relative intensity ratio of the present Raman modes. We find excellent agreement between the two methods...
Nitrogen exhibits an exceptional polymorphism under extreme conditions, making it unique amongst the elemental diatomics and a valuable testing system for experiment-theory comparison. Despite attracting considerable attention, the structures of many high-pressure nitrogen phases still require unambiguous determination. Here, we report the structur...
Through a series of Raman spectroscopy studies, we investigate the behavior of hydrogen-helium and hydrogen-nitrogen mixtures at high pressure across a wide range of concentrations. We find that there is no evidence of chemical association or increased miscibility of hydrogen and helium in the solid state up to pressures of 250 GPa at 300 K. In con...
In situ high-pressure high-temperature synchrotron x-ray diffraction studies of the nickel-hydrogen system reveals the synthesis of a nickel polyhydride, Ni2H3. We observe the formation of NiH at pressures above 1 GPa, which remains stable to 52 GPa at room temperature. Laser heating to above 1000 K at this pressure initiates a transition to a phas...
A recent article by Zhang et al. [Phys. Rev. B 97, 064107 (2018)2469-995010.1103/PhysRevB.97.064107] claimed the high-pressure synthesis and metallization of H3Se, or selenium trihydride, at 23 GPa and 203 K. Here, we demonstrate that the synthesised compound is not H3Se but the previously reported, and already well characterized, (H2Se)2H2. The cl...
We investigate a range of possible materials containing the supermolecular form of hydrogen comprising 13 H2 molecules arranged in an icosahedral arrangement. This supermolecule consists of freely rotating 12 H2 molecules in an icosahedral arrangement, enclosing another freely rotating H2 molecule. To date, this supermolecule has only been observed...
We investigate a range of possible materials containing the supermolecular form of hydrogen comprising 13 hydrogen molecules arranged in an icosahedral arrangement. This supermolecule consists of freely rotating 12 hydrogen molecules in an icosahedral arrangement, enclosing another freely rotating molecule. To date, this supermolecule has only been...
Through a series of Raman spectroscopy studies, we investigate the behaviour of hydrogen-helium and hydrogen-nitrogen mixtures at high pressure across wide ranging concentrations. We find that there is no evidence of chemical association, miscibility, nor any demixing of hydrogen and helium in the solid state up to pressures of 250 GPa at 300 K. In...
Intermetallic lithium compounds have found a wide range of applications owing to their light mass and desirable electronic and mechanical properties. Here, by compressing pure lithium and zinc mixtures in a diamond-anvil cell, we observe a direct reaction forming the stoichiometric compound LiZn, at pressures below 1 GPa. On further compression abo...
A new phase V of hydrogen was recently claimed in experiments above 325 GPa and 300 K. Because of the extremely small sample size at such record pressures the measurements were limited to Raman spectroscopy. The experimental data on increase of pressure show decreasing Raman activity and darkening of the sample, which suggests band gap closure and...
A new phase V of hydrogen was recently claimed in experiments above 325 GPa and 300 K. Due to the extremely small sample size at such record pressures the measurements were limited to Raman spectroscopy. The experimental data on increase of pressure shows decreasing Raman activity and darkening of the sample, which suggests band-gap closure and imp...
High pressure can profoundly affect electronic structure and reactivity, creating compounds between elements that do not react at ambient conditions. Lithium is known to react with gold and silver, however no copper compounds are known to date. By compressing mixtures of the elements in diamond-anvil cells, compounds of lithium and copper have been...
In situ high-pressure high-temperature X-ray powder diffraction studies of the cobalt-hydrogen system reveal the direct synthesis of both the binary cobalt hydride (CoH) and a novel cobalt dihydride (CoH2). We observe the formation of fcc CoH at pressures of 4 GPa, which persists to pressures of 45 GPa. At this pressure, we see the emergence with t...
We have used synchrotron x-ray and Raman spectroscopic studies combined with molecular dynamics to investigate the I2−H2 system at high pressure. By laser heating the mixture above 25 GPa we synthesized the molecular compound HI(H2)13, with the AB13 structure type and unusually high volumetric hydrogen content. The isolation of HI molecules by (H2)...
The observation of high-temperature superconductivity in hydride sulfide (H2S) at high pressures has generated considerable interest in compressed hydrogen-rich compounds. High-pressure hydrogen selenide (H2Se) has also been predicted to be superconducting at high temperatures; however, its behaviour and stability upon compression remains unknown....
Through high-pressure Raman spectroscopy and x-ray diffraction experiments, we have investigated the formation, stability field, and structure of hydrogen iodide (HI). Hydrogen iodide is synthesized by the reaction of molecular hydrogen and iodine at room temperature and at a pressure of 0.2 GPa. Upon compression, HI solidifies into cubic phase I,...
A recent article by Zaghoo et al. [Phys. Rev. B 93, 155128 (2016)] presented high-pressure high-temperature optical experiments claiming the observation of a first-order transition to atomic liquid metallic hydrogen. Here, we demonstrate that the experimental evidence presented is unsubstantial for such a claim. Furthermore, the claimed results and...
In situ high-pressure low-temperature high-quality Raman data for hydrogen and deuterium demonstrate the presence of a novel phase, phase II′, unique to deuterium and distinct from the known phase II. Phase II′ of D2 is not observed in hydrogen, making it the only phase that does not exist in both isotopes and occupies a significant part of P−T spa...
Dias and Silvera (Letters, p. 715, 2017) claim the observation of the Wigner-Huntington transition to metallic hydrogen at 495 GPa. We show that neither the claims of the record pressure or the phase transition to a metallic state are supported by any data and contradict the authors' own unconfirmed previous results.
Dias and Silvera (Letters, p. 715, 2017) claim the observation of the Wigner-Huntington transition to metallic hydrogen at 495 GPa. We show that neither the claims of the record pressure or the phase transition to a metallic state are supported by any data and contradict the authors' own unconfirmed previous results.
Molecular nitrogen exhibits one of the strongest known interatomic bonds, while xenon possesses a closed-shell electronic structure: a direct consequence of which renders both chemically unreactive. Through a series of optical spectroscopy and x-ray diffraction experiments, we demonstrate the formation of a novel van der Waals compound formed from...
Raman spectroscopy and powder x-ray diffraction methods have been used to characterize a novel phase of nitrogen which forms on compression from ambient pressure at low temperatures. The new, λ, phase exhibits an exceptionally wide range of pressure stability from below 1 to 140 GPa, overlapping nine other known phases. On heating, its transformati...
Almost 80 years ago it was predicted that, under sufficient compression, the H-H bond in molecular hydrogen (H 2) would break, forming a new, atomic, metallic, solid state of hydrogen. Reaching this predicted state experimentally has been one of the principal goals in high-pressure research for the past 30 years. Here, using in situ high-pressure R...
An alternative approach to loading metal organic frameworks with gas molecules at high (kbar) pressures is reported. The technique, which uses liquefied gases as pressure transmitting media within a diamond anvil cell along with a single-crystal of a porous metal–organic framework, is demonstrated to have considerable advantages over other gas-load...
The chemical reaction between hydrogen and purely sp2-bonded graphene to form graphene’s purely sp3-bonded analogue, graphane, potentially allows the synthesis of a much wider variety of novel two-dimensional materials by opening a pathway to the application of conventional chemistry methods in graphene. Graphene is currently hydrogenated by exposu...
It has been theorized that at high pressure the increased energy of the zero-point oscillations in hydrogen would destabilize the lattice and form a ground fluid state at 0 K (ref. ). Theory has also suggested that this fluid state, representing a new state of matter, might have unusual properties governed by quantum effects, such as superfluidity...
Using a combination of the Raman spectroscopy and density functional theory calculations on dense hydrogen-deuterium mixtures of various concentrations, we demonstrate that, at 300 K and above 200 GPa, they transform into phase IV, forming a disordered binary alloy with six highly localized intramolecular vibrational (vibrons) and four delocalized...
We employed molecular dynamics simulations together with some novel theoretical techniques to calculate finite temperature Raman spectra in both hydrogen (H) and hydrogen-deuterium (HD) mixtures. By conditioning the simulations with the experimental data, we have discovered the true nature of Phase IV in solid hydrogen. X-ray and neutron diffractio...
We have performed in situ synchrotron x-ray diffraction studies of the iridium-hydrogen system up to 125 GPa. At 55 GPa, a phase transition in the metal lattice from the fcc to a distorted simple cubic phase is observed. The new phase is characterized by a drastically increased volume per metal atom, indicating the formation of a metal hydride, and...
The Raman spectra of compressed hydrogen (deuterium) have been measured in the multi-Mbar pressure range in the diamond anvil cell using the position of the stressed first-order Raman diamond edge (DE) to estimate pressure. We find that the Raman spectra are very consistent in repeated experiments for the critical frequencies of the hydrogen (deute...
A combined experimental and theoretical study has been carried out on the synthesis and characterization of tungsten hydride at high pressures. We confirm the synthesis of tungsten monohydride at above 25 GPa and 300 K. At higher pressures, hydrogen content is found to increase and ab-initio calculations reveal the formation of overstoichiometric t...
Here we review recent experimental and theoretical studies of hydrogen approaching metallization regime. Experimental techniques have made great advances over the last several years making it possible to reach previously unachievable conditions of pressure and temperature and to probe hydrogen at these conditions. Theoretical methods have also grea...
Here we review recent experimental and theoretical studies of hydrogen approaching metallization regime. Ex-perimental techniques have made great advances over the last several years making it possible to reach previously unachievable conditions of pressure and temperature and to probe hydrogen at these conditions. Theoretical me-thods have also gr...
We have studied dense hydrogen and deuterium experimentally up to 320 GPa and
using ab initio molecular dynamic (MD) simulations up to 370 GPa between 250
and 300 K. Raman and optical absorption spectra show significant anharmonic and
quantum effects in mixed atomic and molecular dense phase IV of hydrogen. In
agreement with these observations, ab...
The Silences of the Archives, the Reknown of the Story.
The Martin Guerre affair has been told many times since Jean de Coras and Guillaume Lesueur published their stories in 1561. It is in many ways a perfect intrigue with uncanny resemblance, persuasive deception and a surprizing end when the two Martin stood face to face, memory to memory, befor...
By compressing elemental lithium and hydrogen in a diamond anvil cell, we have synthesized lithium hydride (LiH) at pressures as low as 50 MPa at room temperature. Combined Raman spectroscopy and synchrotron x-ray diffraction measurements reveal that, once synthesized, LiH remains stable at 300 K up to 160 GPa in the presence of molecular hydrogen....
We used Raman and visible transmission spectroscopy to investigate dense hydrogen (deuterium) up to 315 (275) GPa at 300 K. At around 200 GPa, we observe the phase transformation, which we attribute to phase III, previously observed only at low temperatures. This is succeeded at 220 GPa by a reversible transformation to a new phase, IV, characteriz...
High-resolution Raman spectroscopy of dense sodium reveals additonal low-energy lattice excitations in the three high-pressure phases cI16, oP8, and tI19 from 108 to 178 GPa. The Raman-active lattice modes indicate profound changes of the chemical bonding in Na upon its transformation to an insulating state (hP4 phase) at pressures above 178(2) GPa...
