title: The crystal structure of methane B at 8 GPa--an α-Mn arrangement of molecules.
abstract: From a combination of powder and single-crystal synchrotron x-ray diffraction data we have determined the carbon substructure of phase B of methane at a pressure of ∼8 GPa. We find this substructure to be cubic with space group I4¯3m and 58 molecules in the unit cell. The unit cell has a lattice parameter a = 11.911(1) Å at 8.3(2) GPa, which is a factor of √2 larger than had previously been proposed by Umemoto et al. [J. Phys.: Condens. Matter 14, 10675 (2002)]. The substructure as now solved is not related to any close-packed arrangement, contrary to previous proposals. Surprisingly, the arrangement of the carbon atoms is isostructural with that of α-manganese at ambient conditions.
authors.affiliation: SUPA, School of Physics and Astronomy and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom.
authors.forename: H E
authors.initials: HE
authors.lastname: Maynard-Casely
authors.affiliation: SUPA, School of Physics and Astronomy and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom.
authors.forename: L F
authors.initials: LF
authors.lastname: Lundegaard
authors.affiliation: SUPA, School of Physics and Astronomy and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom.
authors.forename: I
authors.initials: I
authors.lastname: Loa
authors.affiliation: SUPA, School of Physics and Astronomy and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom.
authors.forename: M I
authors.initials: MI
authors.lastname: McMahon
authors.affiliation: SUPA, School of Physics and Astronomy and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom.
authors.forename: E
authors.initials: E
authors.lastname: Gregoryanz
authors.affiliation: SUPA, School of Physics and Astronomy and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom.
authors.forename: R J
authors.initials: RJ
authors.lastname: Nelmes
authors.affiliation: SUPA, School of Physics and Astronomy and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom.
authors.forename: J S
authors.initials: JS
authors.lastname: Loveday