The crystal structure of methane B at 8 GPa--an α-Mn arrangement of molecules

H E Maynard-Casely; L F Lundegaard; I Loa; M I McMahon; E Gregoryanz; R J Nelmes; J S Loveday

doi:10.1063/1.4903813

The crystal structure of methane B at 8 GPa--an α-Mn arrangement of molecules

J Chem Phys. 2014 Dec 21;141(23):234313. doi: 10.1063/1.4903813.

Authors

H E Maynard-Casely¹, L F Lundegaard¹, I Loa¹, M I McMahon¹, E Gregoryanz¹, R J Nelmes¹, J S Loveday¹

Affiliation

¹ SUPA, School of Physics and Astronomy and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom.

PMID: 25527941
DOI: 10.1063/1.4903813

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.