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Title: Unusually complex phase of dense nitrogen at extreme conditions

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:
Grant/Contract Number:
AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
Nature Communications
Additional Journal Information:
Journal Volume: 9; Journal Issue: 1; Journal ID: ISSN 2041-1723
Publisher:
Nature Publishing Group
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE
OSTI Identifier:
1490646

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., 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. 2018. "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},
number = 1,
volume = 9,
place = {United States},
year = {2018},
month = {11}
}

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