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Title: Unusually complex phase of dense nitrogen at extreme conditions

Abstract

Here, 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 structure of the elusive high-pressure high-temperature polymorph ι–N 2 at 56 GPa and ambient temperature, determined by single crystal X-ray diffraction, and investigate its properties using ab initio simulations. We find that ι–N 2 is characterised by an extraordinarily large unit cell containing 48 N 2 molecules. Geometry optimisation favours the experimentally determined structure and density functional theory calculations find ι–N 2 to have the lowest enthalpy of the molecular nitrogen polymorphs that exist between 30 and 60 GPa. The results demonstrate that very complex structures, similar to those previously only observed in metallic elements, can become energetically favourable in molecular systems at extreme pressures and temperatures.

Authors:
ORCiD logo [1];  [2]; ORCiD logo [3];  [1]; ORCiD logo [4];  [1];  [3]; ORCiD logo [5]
  1. Univ. of Edinburgh, Edinburgh (United Kingdom)
  2. European Synchrotron Radiation Facility, Grenoble (France)
  3. Center for High Pressure Science & Technology Advanced Research, Shanghai (China)
  4. Univ. of Edinburgh, Edinburgh (United Kingdom); SLAC National Accelerator Lab., Menlo Park, CA (United States)
  5. Chinese Academy of Sciences, Hefei (China)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1490646
Grant/Contract Number:  
AC02-76SF00515
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nature Communications
Additional Journal Information:
Journal Volume: 9; Journal Issue: 1; Journal ID: ISSN 2041-1723
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Turnbull, Robin, Hanfland, Michael, Binns, Jack, Martinez-Canales, Miguel, Frost, Mungo, Marqués, Miriam, Howie, Ross T., and Gregoryanz, Eugene. Unusually complex phase of dense nitrogen at extreme conditions. United States: N. p., 2018. Web. doi:10.1038/s41467-018-07074-4.
Turnbull, Robin, Hanfland, Michael, Binns, Jack, Martinez-Canales, Miguel, Frost, Mungo, Marqués, Miriam, Howie, Ross T., & Gregoryanz, Eugene. Unusually complex phase of dense nitrogen at extreme conditions. United States. doi:10.1038/s41467-018-07074-4.
Turnbull, Robin, Hanfland, Michael, Binns, Jack, Martinez-Canales, Miguel, Frost, Mungo, Marqués, Miriam, Howie, Ross T., and Gregoryanz, Eugene. Fri . "Unusually complex phase of dense nitrogen at extreme conditions". United States. doi:10.1038/s41467-018-07074-4. https://www.osti.gov/servlets/purl/1490646.
@article{osti_1490646,
title = {Unusually complex phase of dense nitrogen at extreme conditions},
author = {Turnbull, Robin and Hanfland, Michael and Binns, Jack and Martinez-Canales, Miguel and Frost, Mungo and Marqués, Miriam and Howie, Ross T. and Gregoryanz, Eugene},
abstractNote = {Here, 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 structure of the elusive high-pressure high-temperature polymorph ι–N2 at 56 GPa and ambient temperature, determined by single crystal X-ray diffraction, and investigate its properties using ab initio simulations. We find that ι–N2 is characterised by an extraordinarily large unit cell containing 48 N2 molecules. Geometry optimisation favours the experimentally determined structure and density functional theory calculations find ι–N2 to have the lowest enthalpy of the molecular nitrogen polymorphs that exist between 30 and 60 GPa. The results demonstrate that very complex structures, similar to those previously only observed in metallic elements, can become energetically favourable in molecular systems at extreme pressures and temperatures.},
doi = {10.1038/s41467-018-07074-4},
journal = {Nature Communications},
issn = {2041-1723},
number = 1,
volume = 9,
place = {United States},
year = {2018},
month = {11}
}

Journal Article:
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Cited by: 2 works
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Figures / Tables:

Fig. 1 Fig. 1: The nitrogen phase and reaction diagram. a The reported P–T paths to the high-temperature molecular phases ι–N2 and θ–N2 are shown with dotted and dashed arrows respectively. The red shaded region approximates the known stability field of ι–N2 based on a combination of our Raman measurements and thosemore » of ref.12. Path 1: Isobaric heating of ε–N2 to 750 K at 65 GPa, as performed in this study. Path 2: Isothermal decompression of θ–N2 to 69 GPa at 850 K. P–T paths and data points are taken from refs.11,12,21,22 which identify the phases through Raman spectroscopy. Black phase-boundaries are based on refs.21–23. Phases α, β, γ, δ*, ζ', κ and λ–N2 are omitted for clarity. b–d Micrographs of the visual changes across the ε–N2→ ι–N2 phase transition. The sample is approximately 60 μm in diameter and 15 μm thick. The time from the onset of the phase-transition is shown on each frame. The arrows in c indicate the progression of the ε–N2→ ι–N2 phase boundary. e Vibrational Raman spectrum of ι–N2 once recovered to ambient temperature. The inset spectrum (light grey) shows ν1 scaled by a factor of 0.05 to display it fully« less

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Works referenced in this record:

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    Works referencing / citing this record:

    CSD 1869044: Experimental Crystal Structure Determination: Non-CSD Structure
    dataset, September 2018


      Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.