High-Pressure Phases of a S-Based Compound: Dimethyl Sulfide

Abstract

The high-pressure behavior of dimethyl sulfide was investigated at room temperature by Raman scattering measurements with pressures up to 30.1 GPa. Phase transitions at 1.3, 3.6-5.8, and 17.2 GPa were found and evidenced by the frequency shifts, pressure coefficients, and changes in fwhm of related modes. These phase transitions were suggested to result from the changes in the inter- and intramolecular bonding of the material. Interestingly, the CH groups was compelled to be frozen in positions at a relatively low pressure, suggested by the disappearance of the relative modes softening. In addition, the appearance of lattice mode can also be found at a modest pressure, which makes it possible to gain a superiority for this compound to further investigate the superconductivity with high transition temperatures of bulk hydrogen.

Raman spectroscopy studies on dimethyl selenium at pressures of up to 40.6 GPa

“…With further increasing pressure up to 40.6 GPa, Mode ν 2 seems to become “fat” quickly, which suggests that DMSe starts to solidify by compression . Compared to the (CH 3 ) 2 S at high pressure, C–Se stretch modes in this region behave very humble, and reversal change in both modes as a result of Fermi resonance is not found, which is evidence for the stable symmetry assignment in this crystal phase.…”

“…This provides further evidence for the solid–solid phase transition at this pressure. Additionally, it is found that the peaks of Modes ν 7 and ν 8 maintain stable, only broadened and weakened, and Mode ν 8 nearly vanishes with pressure up to 40.6 GPa, which is totally different from the (CH 3 ) 2 S at this region …”

“…It is a general rule that an increase in pressure should increase the A–H bond wavenumbers of weak and medium‐strength hydrogen bonds; however, the appearance of the softening behavior has been a characteristic in hydrogen‐rich compounds containing CH 3 or NH 3 groups where order–disorder transitions take place with temperature or pressure. For example, the pressure‐induced restricted rotation of NH 3 groups and the locked NH 3 positions in the compounds of dihydrogen bonding molecule of NH 3 BH 3 , CH 3 HgM (M = Cl, Br, and I), (CH 3 ) 2 XM (X = Sn or Tl), X(CH 3 ) 4 (X = Si, Ge, and Sn), and (CH 3 ) 2 S can be reflected by the softening of CH 3 vibrational mode in the Raman spectra. For the CH 3 HgM (M = Cl, Br, and I), this softening behavior existed with the pressure up to 0.59 GPa for CH 3 HgCl, 1.25 GPa for CH 3 HgBr, and 0.5 GPa for CH 3 HgI, respectively.…”

“…For the Si(CH 3 ) 4 , this softening behavior existed with the pressure up to 9.0 GPa, whereas it is 1.4 and 0.9 GPa for Ge(CH 3 ) 4 and Sn(CH 3 ) 4 , respectively, which suggests that the appearance of such softening behavior needs more low pressure in the homologous compounds with heavier atoms. Compared with these results, (CH 3 ) 2 S is very easy to undergo phase transition via active rotation of the CH 3 groups to freezing in a position only at 3.6 GPa, then is there a possibility that the softening behavior from the CH 3 groups of DMSe has been done at 0.4 GPa? Obviously, CH 3 groups in the DMSe must have a unique vibrational style upon compression taking account of the anomalous behavior of CH 3 groups, which always exists in the whole pressure process.…”

“…Therefore, it seems worthwhile to investigate the high‐temperature superconductivity of hydrogen‐rich compounds where interactions between the CH 3 groups and Group VIa element exist. For example, our recent investigation on the pressure‐induced phases of the dimethyl sulfide ((CH 3 ) 2 S)) by Raman spectroscopy found a softening behavior and lattice modes that appeared much earlier compared with the cases in Si(CH 3 ) 4 with increasing pressure, suggesting that such material possesses a potential possibility to achieve superconductivity with high‐transition temperatures yet at lower pressures. Additionally, it is suggested that the homologous hydrides with heavier atoms would yield lower metallization pressure, due to the weaker chemical bonds that can be dissociated at high pressures .…”