Exploring high-pressure transformations in low-Z (H2, Ne) hydrates at low temperatures

Paulo H.B. Brant Carvalho, Amber Mace, Inna Martha Nangoi, Alexandre A. Leitão, Chris A. Tulk, Jamie J. Molaison, Ove Andersson, Alexander P. Lyubartsev, Ulrich Häussermann

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5 Scopus citations

Abstract

The high pressure structural behavior of H2 and Ne clathrate hydrates with approximate composition H2/Ne·~4H2O and featuring cubic structure II (CS-II) was investigated by neutron powder diffraction using the deuterated analogues at ~95 K. CS-II hydrogen hydrate transforms gradually to isocompositional C1 phase (filled ice II) at around 1.1 GPa but may be metastably retained up to 2.2 GPa. Above 3 GPa a gradual decomposition into C2 phase (H2·H2O, filled ice Ic) and ice VIII’ takes place. Upon heating to 200 K the CS-II to C1 transition completes instantly whereas C1 decomposition appears sluggish also at 200 K. C1 was observed metastably up to 8 GPa. At 95 K C1 and C2 hydrogen hydrate can be retained below 1 GPa and yield ice II and ice Ic, respectively, upon complete release of pressure. In contrast, CS-II neon hydrate undergoes pressure-induced amorphization at 1.9 GPa, thus following the general trend for noble gas clathrate hydrates. Upon heating to 200 K amorphous Ne hydrate crystallizes as a mixture of previously unreported C2 hydrate and ice VIII’.

Original languageEnglish
Article number9
JournalCrystals
Volume12
Issue number1
DOIs
StatePublished - Jan 2022

Funding

Funding: This research has been funded by the Swedish Foundation for Strategic Research (SSF) within the Swedish national graduate school in neutron scattering (SwedNess). A portion of this research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. The simulations were enabled by resources provided by the Swedish National Infrastructure for Computing (SNIC), partially funded by the Swedish Research Council through grant agreement no. 2018-05973. The authors thank also the financial support from the Swedish Foundation for International Cooperation in Research and Higher Education (STINT) and the Brazilian agency CAPES (project CAPES/STINT N◦ 88887.304724/2018). This research has been funded by the Swedish Foundation for Strategic Research (SSF) within the Swedish national graduate school in neutron scattering (SwedNess). A portion of this research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. The simulations were enabled by resources provided by the Swedish National Infrastructure for Computing (SNIC), partially funded by the Swedish Research Council through grant agreement no. 2018-05973. The authors thank also the financial support from the Swedish Foundation for International Cooperation in Research and Higher Education (STINT) and the Brazilian agency CAPES (project CAPES/STINT N? 88887.304724/2018).

Keywords

  • Clathrate hydrates
  • Hydrogen hydrate
  • Molecular dynamics
  • Neon hydrate
  • Neutron diffraction
  • Pressure effects

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