title: Synthesis of sodium polyhydrides at high pressures.
abstract: The only known compound of sodium and hydrogen is archetypal ionic NaH. Application of high pressure is known to promote states with higher atomic coordination, but extensive searches for polyhydrides with unusual stoichiometry have had only limited success in spite of several theoretical predictions. Here we report the first observation of the formation of polyhydrides of Na (NaH3 and NaH7) above 40 GPa and 2,000 K. We combine synchrotron X-ray diffraction and Raman spectroscopy in a laser-heated diamond anvil cell and theoretical random structure searching, which both agree on the stable structures and compositions. Our results support the formation of multicenter bonding in a material with unusual stoichiometry. These results are applicable to the design of new energetic solids and high-temperature superconductors based on hydrogen-rich materials.
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington, District of Columbia 20015, USA.
authors.forename: Viktor V
authors.initials: VV
authors.lastname: Struzhkin
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington, District of Columbia 20015, USA.|Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, China.
authors.forename: Duck Young
authors.initials: DY
authors.lastname: Kim
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington, District of Columbia 20015, USA.|Lawrence Livermore National Laboratory, Material Sciences Division, 7000 East Avenue, L-350, Livermore, CA 94550-9698, USA.
authors.forename: Elissaios
authors.initials: E
authors.lastname: Stavrou
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington, District of Columbia 20015, USA.
authors.forename: Takaki
authors.initials: T
authors.lastname: Muramatsu
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington, District of Columbia 20015, USA.|Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, China.
authors.forename: Ho-Kwang
authors.initials: HK
authors.lastname: Mao
authors.affiliation: Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK.|Department of Materials Science &Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, UK.
authors.forename: Chris J
authors.initials: CJ
authors.lastname: Pickard
authors.affiliation: Theory of Condensed Matter Group, Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE, UK.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Needs
authors.affiliation: Center for Advanced Radiation Sources, The University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Vitali B
authors.initials: VB
authors.lastname: Prakapenka
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington, District of Columbia 20015, USA.|Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei, Anhui 230031, China.
authors.forename: Alexander F
authors.initials: AF
authors.lastname: Goncharov