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. 2014 Nov 10:4:6968.
doi: 10.1038/srep06968.

Pressure-induced metallization of dense (H₂S)₂H₂ with high-Tc superconductivity

Defang Duan  1 , Yunxian Liu  2 , Fubo Tian  2 , Da Li  2 , Xiaoli Huang  2 , Zhonglong Zhao  2 , Hongyu Yu  2 , Bingbing Liu  2 , Wenjing Tian  3 , Tian Cui  2
Affiliations

Pressure-induced metallization of dense (H₂S)₂H₂ with high-Tc superconductivity

Defang Duan et al. Sci Rep. .

Abstract

The high pressure structures, metallization, and superconductivity of recently synthesized H2-containing compounds (H2S)2H2 are elucidated by ab initio calculations. The ordered crystal structure with P1 symmetry is determined, supported by the good agreement between theoretical and experimental X-ray diffraction data, equation of states, and Raman spectra. The Cccm structure is favorable with partial hydrogen bond symmetrization above 37 GPa. Upon further compression, H2 molecules disappear and two intriguing metallic structures with R3m and Im-3m symmetries are reconstructive above 111 and 180 GPa, respectively. The predicted metallization pressure is 111 GPa, which is approximately one-third of the currently suggested metallization pressure of bulk molecular hydrogen. Application of the Allen-Dynes-modified McMillan equation for the Im-3m structure yields high Tc values of 191 K to 204 K at 200 GPa, which is among the highest values reported for H2-rich van der Waals compounds and MH3 type hydride thus far.

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Figures

Figure 1
Figure 1. High-pressure crystal structures of (H2S)2H2.
(a) P1 structure normal to the (001) plane, (b) P1 structure normal to the (010) plane, (c) Cccm structure normal to the (001) plane, (c) Cccm structure normal to the (100) plane, (e) R3m, and (f) Im-3m. Large spheres represent S and small spheres denote H atoms, respectively.
Figure 2
Figure 2. Calculated enthalpies per H3S unit as the function of pressure.
Calculated enthalpy curves for various structures relative to our predicted Cccm structure as a function of pressure. The decomposition enthalpies into S+3/2H2 and H2S+1/2H2 are also plotted.
Figure 3
Figure 3. Calculated XRD and EOS compared with experiment data.
(a) The simulated XRD patterns and (b) calculated EOS for the P1 structures compared with experiment data (ref. 2). (c) Various interatomic distances of P1, Cccm, R3m, and Im-3m structures with pressure.
Figure 4
Figure 4. Electronic band structure and density of states (DOS).
Electronic band structure and atom-projected DOS for (a) R3m at 130 GPa and (b) Im-3m at 200 GPa along the selected high symmetry lines, where the dotted lines at zero indicate the Fermi level.
Figure 5
Figure 5. Phonon properties and Eliashberg spectral function.
Phonon dispersion curves, phonon density of states (PHDOS) projected on S and H atoms, and Eliashberg spectral function α2F(ω) together with the electron-phonon integral λ(ω) for (a) R3m at 130 GPa and (b) Im-3m at 200 GPa.
Figure 6
Figure 6. Calculated ELF of (H2S)2H2.
The calculated ELF of (a) R3m with isosurface value of 0.73, (b) R3m for the (011) plane, (c) Im-3m with isosurface value of 0.73, (d) Im-3m for (100) plane.
See this image and copyright information in PMC

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