Structural and vibrational properties of methane up to 71 GPa

Change log
Bykov, M 
Bykova, E 
Pickard, CJ 
Martinez-Canales, M 
Glazyrin, K 

Single-crystal synchrotron X-ray diffraction, Raman spectroscopy, and first principles calculations have been used to identify the structure of the high-pressure (HP) phase of molecular methane above 20 GPa up to 71 GPa. The structure of HP phase is trigonal R3, which can be represented as a distortion of the cubic phase B, previously documented at 7-15 GPa and confirmed here. The positions of hydrogen atoms in HP phase have been obtained from first principles calculations. The molecules occupy four different crystallographic sites in phases B and eleven sites in the HP phase, which result in splitting of molecular stretching modes detected in Raman spectroscopy and assigned here based on a good agreement with the Raman spectra calculated from the first principles. Our study points out to a single HP phase unlike up to three HP phases proposed previously based on the Raman spectroscopy results only.

51 Physical Sciences, 34 Chemical Sciences, 3406 Physical Chemistry
Journal Title
Physical Review B
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American Physical Society (APS)
Engineering and Physical Sciences Research Council (EP/P022596/1)