title: Backbone NxH compounds at high pressures.
abstract: Optical and synchrotron x-ray diffraction diamond anvil cell experiments have been combined with first-principles theoretical structure predictions to investigate mixtures of N2 and H2 up to 55 GPa. Our experiments show the formation of structurally complex van der Waals compounds [see also D. K. Spaulding et al., Nat. Commun. 5, 5739 (2014)] above 10 GPa. However, we found that these NxH (0.5 < x < 1.5) compounds transform abruptly to new oligomeric materials through barochemistry above 47 GPa and photochemistry at pressures as low as 10 GPa. These oligomeric compounds can be recovered to ambient pressure at T < 130 K, whereas at room temperature, they can be metastable on pressure release down to 3.5 GPa. Extensive theoretical calculations show that such oligomeric materials become thermodynamically more stable in comparison to mixtures of N2, H2, and NH3 above approximately 40 GPa. Our results suggest new pathways for synthesis of environmentally benign high energy-density materials. These materials could also exist as alternative planetary ices.
authors.affiliation: Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, 350 Shushanghu Road, Hefei, Anhui 230031, China.
authors.forename: Alexander F
authors.initials: AF
authors.lastname: Goncharov
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, Washington, D.C. 20015, USA.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Holtgrewe
authors.affiliation: Department of Geosciences, State University of New York, Stony Brook, New York 11794-2100, USA.
authors.forename: Guangrui
authors.initials: G
authors.lastname: Qian
authors.affiliation: Guangxi Key Laboratory of Information Materials, Guilin University of Electronic Technology, Guilin 541004, China.
authors.forename: Chaohao
authors.initials: C
authors.lastname: Hu
authors.affiliation: Skolkovo Institute of Science and Technology, Skolkovo Innovation Center, Moscow 143026, Russia.
authors.forename: Artem R
authors.initials: AR
authors.lastname: Oganov
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, Washington, D.C. 20015, USA.
authors.forename: Maddury
authors.initials: M
authors.lastname: Somayazulu
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, Washington, D.C. 20015, USA.
authors.forename: Elissaios
authors.initials: E
authors.lastname: Stavrou
authors.affiliation: University College London, Gower St., London WC1E 6BT, United Kingdom.
authors.forename: Chris J
authors.initials: CJ
authors.lastname: Pickard
authors.affiliation: Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, 350 Shushanghu Road, Hefei, Anhui 230031, China.
authors.forename: Adam
authors.initials: A
authors.lastname: Berlie
authors.affiliation: Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, 350 Shushanghu Road, Hefei, Anhui 230031, China.
authors.forename: Fei
authors.initials: F
authors.lastname: Yen
authors.affiliation: Howard University, Washington, D.C. 20059, USA.
authors.forename: Mahmood
authors.initials: M
authors.lastname: Mahmood
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, Washington, D.C. 20015, USA.
authors.forename: Sergey S
authors.initials: SS
authors.lastname: Lobanov
authors.affiliation: DESY Photon Science, Notkestrasse 85, D-22607 Hamburg, Germany.
authors.forename: Zuzana
authors.initials: Z
authors.lastname: Konôpková
authors.affiliation: Center for Advanced Radiation Sources, University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Vitali B
authors.initials: VB
authors.lastname: Prakapenka