A high-pressure van der Waals compound in solid nitrogen-helium mixtures

  title={A high-pressure van der Waals compound in solid nitrogen-helium mixtures},
  author={Willem L. Vos and Larry W. Finger and Russell J. Hemley and J. Z. Hu and Ho-kwang Mao and Jan A. Schouten},
WEAKLY bound van der Waals molecules, consisting of atoms or molecules (such as rare gases, H2 and N2) interacting through van der Waals forces, can be formed in the gas phase1. The existence of similar weakly bound stoichiometric compounds in condensed phases has remained an open question as the components usually form separate pure phases or solid solutions2. Here we report on a detailed study of the helium–nitrogen system in a diamond-anvil cell using synchrotron X-ray diffraction, Raman… Expand
Pressure-induced bonding and compound formation in xenon-hydrogen solids.
The formation of a stable compound in the Xe-H(2) binary system is described by a suite of X-ray diffraction and optical spectroscopy measurements, indicating a weakening of the intramolecular covalent bond as well as persistence of semiconducting behaviour in the compound to at least 255 GPa. Expand
Stability of van der Waals compounds and investigation of the intermolecular potential in helium–xenon mixtures
The stability of the stoichiometric solid structures Xe(He)2 and Xe(He)13 is investigated up to 30 GPa pressure at room temperature, T=300 K. The Gibbs free energy of these so‐called van der WaalsExpand
The role of van der Waals and exchange interactions in high-pressure solid hydrogen.
  • S. Azadi, G. Ackland
  • Chemistry, Materials Science
  • Physical chemistry chemical physics : PCCP
  • 2017
It is concluded that, in addition to the vdW interaction, a correct treatment of the high charge gradient limit is essential and the dependence of molecular bond-lengths on exchange-correlation also has a considerable influence on the calculated metallization pressure. Expand
Coexistence of plastic and partially diffusive phases in a helium-methane compound
Helium and methane are major components of giant icy planets and are abundant in the universe. However, helium is the most inert element in the periodic table and methane is one of the mostExpand
Multiple superionic states in helium–water compounds
Superionic states are phases of matter that can simultaneously exhibit some of the properties of a liquid and of a solid. For example, in superionic ice, hydrogen atoms can move freely while oxygenExpand
Structural and vibrational properties of condensed phases in xenon molecular binary systems: He-Xe, H2-Xe
We present both structural and vibrational (Raman) results of compressed xenon binary systems of He and H2 to a maximum pressure of 142 GPa. In the He-Xe mixture 15% vol. Xe and balance He, weExpand
High-Pressure Compounds in Methane-Hydrogen Mixtures
The effect of pressure on chemical interactions in molecular mixtures is important for problems spanning fundamental chemistry, planetary science, and materials science. Diamond-anvil cell studiesExpand
Electrostatic force driven helium insertion into ammonia and water crystals under pressure
Helium, ammonia and ice are among the major components of giant gas planets, and predictions of their chemical structures are therefore crucial in predicting planetary dynamics. Here we demonstrate aExpand
Structure and stability of solid Xe(H2)n.
The synchrotron x-ray diffraction and Raman measurements show that this unique hydrogen-bearing compound that can be synthesized at 4.2 GPa and 300 K, quenched at low temperatures to atmospheric pressure, and retained up to 90 K on subsequent warming. Expand
Comparison of the high-pressure and low-temperature structures of sulfuric acid
We have determined the high-pressure crystal-structure of sulfuric acid, including the positions of the hydrogen atoms, using a combination of single-crystal X-ray diffraction techniques and abExpand


High-pressure phase diagram and equation of state of solid helium from single-crystal x-ray diffraction to 23.3 GPa.
  • Mao, Hemley, +4 authors Bassett
  • Materials Science, Medicine
  • Physical review letters
  • 1988
Single-crystal X-ray diffraction measurements on solid He-4 demonstrate that the structure of the solid is hexagonal close packed over this pressure-temperature range, contrary to both the interpretation of high-pressure optical studies and to theoretical predictions. Expand
Prediction of fluid–fluid and fluid–solid equilibria in the molecular system helium–hydrogen up to 1 Mbar
By using variational theory together with an extended van der Waals one‐fluid model, as has been developed by Ree, fluid–fluid coexistence surfaces of He–H2 mixtures are calculated up to 1 Mbar. TheExpand
Refractive-index measurements of dense helium up to 16 GPa at T=298 K: Analysis of its thermodynamic and electronic properties.
The refractive index of He as a function of pressure, n(P), has been measured by an experimental procedure which couples two types of interferometric methods, and the equation of state is extrapolated into the solid phase, in good agreement with recent single-crystal x-ray data. Expand
Fluid-fluid, fluid-solid and three-phase equilibria in the system helium-hydrogen at pressures up to 75 kbar
The phase diagram of the system helium-hydrogen has been studied, using the diamond anvil cell technique, in a pressure range from 15 to 75 kbar and at temperatures from 110 up to 360 K. TheExpand
A model for the freezing of binary colloidal hard spheres
Phase boundaries are calculated for the freezing of a binary mixture of colloidal hard spheres which are assumed to be immiscible in a single solid phase. Results are reported for mixtures ofExpand
Synchrotron X-ray Diffraction Measurements of Single-Crystal Hydrogen to 26.5 Gigapascals
The crystal structure and equation of state of solid hydrogen have been determined directly to 26.5 gigapascals at room temperature by new synchrotron x-ray diffraction techniques, removing the discrepancy between earlier indirect determinations and providing a new experimental constraint on the molecular-to-atomic transition predicted at higher pressures. Expand
Phase equilibria in binary systems at very high pressures
Abstract The development of the diamond anvil cell technique extended the experimental pressure range for static measurements of physical properties of substances considerably. In this paper, theExpand
Structures and phase diagrams of N2 and CO to 13 GPa by x‐ray diffraction
The structures and phase transitions of N2 and CO were studied by powder x‐ray diffraction from 100 to 300 K and 4 to 13 GPa. Three solid phases, β, δ, and e, were observed in each material. TheExpand
High pressure x‐ray diffraction studies on solid N2 up to 43.9 GPa
Solid N2 was studied by energy‐dispersive x‐ray diffraction between 5.75 and 43.9 GPa at room temperature. The transition from δ‐N2 (Pm3n) to e‐N2 (R3c) was observed at 16.3±0.5 GPa. TheExpand
The phase diagram of the binary mixture nitrogen-helium at high pressure
As part of a systematic study of binary mixtures at high pressures, the system nitrogen-helium has been studied with a diamond anvil cell, using visual observation and quasi-isochoricExpand