Favored decomposition paths of hydrogen sulfide at high pressure

Abstract

Sulfur trihydride (H 3 S) is a theoretically predicted high-pressure superconductor and has been experimentally confirmed to have the highest superconducting transition temperature T c . Solid H 2 S decomposition is considered as the primary source of H 3 S, however, it is complex and controversial how H 2 S is transformed into H 3 S. Herein, we employ the density functional theory augmented with many-body dispersion interactions (DFT+MBD) to study a full path of H 2 S decomposition at pressure of 20-260 GPa. We find that H 2 S starts to decompose into H 3 S and other H-S compounds from about 20 GPa, in which the MBD interactions can decrease both the phase transition pressure of H-S compounds and the reaction transition pressure of H 2 S decomposition. H 3 S 2 , H 4 S 3 , H 3 S 5 , sulfur and HS 2 are byproducts of H 2 S decomposition with increasing pressure. Our results provide a complete phase diagram of H-S compounds during H 2 S decomposition, and clarify the pressure range of each product and favored paths of H 2 S decomposition.

Properties and phase diagram of (H2S)2H2

“…‡ e.gregoryanz@ed.ac.uk found competitive H-S stoichiometries (e.g., H 5 S 2 ) present 48 with H 3 S, close to the pressures where the highest T c is 49 claimed [1,11]. Disproportionated S and other by-products 50 imply that the H 3 S product from H 2 S is impure, which may 51 account for inconsistent T c measurements (ranging from 110 52 to 203 K) reported in experiments using H 2 S as a precursor 53 [1,[18][19][20][21].…”

“…The report of high-temperature superconductivity in dense H 2 S has galvanized studies of the high-pressure sulfurhydrogen system [1], yet the composition and nature of bonding in the superconducting phase remain disputed [2][3][4][5][6][7][8][9][10][11].…”

“…9). Despite the fact that competitive H 3 S structures have been reported in the relevant pressure ranges (e.g., C2/c) [11], Cccm still presents the best stable structural candidate for phase III, which agrees with the experimental Raman data [13,41]; Cccm has two H 2 environments compared to the single environment of I4/mcm [15], and the predicted H-H bond lengths as a function of pressure for Cccm also correspond very well to the observed frequency dependences of ν IIIa/b [13] [Figs. 1, 2(a), 5, and 6].…”

Novel sulfur hydrides synthesized at extreme conditions

“…In the XRD patterns at relevant pressures and temperatures, the diffraction of nanocrystalline diamond was observed, inferring that it is, along with H, a decomposition of paraffin oil. Also, the unitcell, space group, and sulfur atom arrangement of the tI140 and hP112 compounds were compared against the H-S solids previously theoretically predicted, including those identified as potential decomposition products of H 2 S [21,22], and no match was found.…”

“…Im-3m) [15][16][17][18][19]. Observing exclusively the sulfur-hydrogen compound with the H 3 S stoichiometry is strikingly at odds with convex hull calculations on the S-H system [21,22]. Indeed, whereas in the pressure range of 40-150 GPa H 3 S always appears on the convex hull as the H-richest phase, a variety of phases with a lower hydrogen content, such as HS 2 , H 3 S 5 , H 5 S 8 , H 4 S 3 , and H 3 S 2 [21,22], have been predicted.…”