X-ray diffraction studies and equation of state of methane at 202GPa

Sun, Liling; Yi, Wei; Wang, Lin; Shu, Jinfu; Sinogeikin, Stas; Meng, Yue; Shen, Guoyin; Bai, Li; Li, Yanchuan; Liu, Jing; Mao, Ho‐kwang; Mao, Wendy L.

doi:10.1016/j.cplett.2009.03.072

Cited by 45 publications

(69 citation statements)

References 16 publications

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“…Its unit cell has been determined to be cubic with a lattice parameter of a = 7.914 Å at 16.9 GPa. 7 This simple cubic unit cell has been used to interpret a number of subsequent powder diffraction studies 15,16 and as a basis for computational studies. 17 A recent theoretical study claimed to have identified a cubic structure of methane with space group I43m below 14 GPa from first-principle calculations, 18 but provided no lattice parameters or atomic co-ordinates for this structure.…”

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confidence: 99%

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

Maynard-Casely

Lundegaard

Loa

et al. 2014

The Journal of Chemical Physics

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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 $I\bar 43m$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.

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Section: Introductionmentioning

confidence: 99%

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

Maynard-Casely

Lundegaard

Loa

et al. 2014

The Journal of Chemical Physics

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“…However, this structural change was not detected by an independent x-ray diffraction measurement. 15 The differing results from studying methane at 25 GPa makes the existence of a phase transformation at that pressure range debatable.…”

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Raman study of phase transitions in compressed methane using moissanite anvil cells

Chen¹,

Zha

Chen

et al. 2011

Phys. Rev. B

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Thorough investigations using Raman spectra of solid methane (CH4) were conducted using moissanite anvil cells in the range of 1−43 GPa at room temperature to identify high-pressure phases. Two novel phases that are distinguishable from previously reported phases were uncovered. One, with a narrow pressure range of 1 GPa centered at around 12.5 GPa and another, with a range of 3 GPa centered around 40.5 GPa. Our results do not support the existence of a phase transformation around 25 GPa. The high quality Raman spectra, obtained by using single crystal samples, narrow the boundaries of seven methane phases at pressures up to 43.2 GPa.

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“…(1), B 0 is the isothermal bulk modulus at zero pressure, B' 0 is the pressure derivative of B 0 at zero pressure and (V/V 0 ) is the ratio of the volume at high pressure to that at zero pressure. On comparing our data for pressure-volume values to that obtained in [32] by using experimental EOS mentioned in Eq. (1), we notice that our calculations agree very well with the reported values ( Figure 3).…”

Section: Resultsmentioning

confidence: 99%

First-principles study of solid methane at high pressure

2014

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We study the structural and electronic properties of solid methane of space group P2 1 2 1 2 1 at high pressure. The density-functional theory (DFT) based first-principles calculations within the Generalized Gradient Approximations (GGA) have been performed by using Quantum Espresso package. Our findings show that the solid methane in orthorhombic structure compresses fast at the first, and then slowly as a function of elevated hydrostatic pressure. The pressure-volume diagram agrees with the available previously reported data up to pressure of around 200 GPa. In orthorhombic structure, solid methane is a wide band gap insulator at low pressures (tens of GPa). The band gap decreases with increase in the pressure. At high pressure (around 900 GPa), the band gap decreases to semi-conductor range (1.78 eV). Our results reveal that methane to be metallic above the pressure coverage of the present study which is consistent to the interior of the giant planets. The band gap as a function of pressure (from the present work) agrees well with the previously reported data.

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X-ray diffraction studies and equation of state of methane at 202GPa

Cited by 45 publications

References 16 publications

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

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

Raman study of phase transitions in compressed methane using moissanite anvil cells

First-principles study of solid methane at high pressure

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