| H3S | |
|---|---|
| Name | H3S |
| Caption | Schematic depiction of a hydrogen-rich sulfur unit cell under pressure |
| Formula | H3S |
| Molar mass | 34.11 g·mol−1 |
| Appearance | colorless gas (at ambient, hypothetical) |
| Density | variable with phase |
| Phase | solid (high-pressure phases) |
| Discovery | theoretical prediction and high-pressure experiment (2014–2015) |
| Related | H2S, SH3 (ion), H5S2 |
H3S H3S is a chemical stoichiometry and structural motif referring to hydrogen-rich sulfur compounds commonly discussed in high-pressure condensed matter physics and quantum chemistry. It became prominent through theoretical predictions and experimental studies linking hydrogen–sulfur compounds to high-temperature superconductivity under extreme pressure, making it a model system for testing BCS theory extensions, electron–phonon coupling calculations, and high-pressure synthesis methods.
H3S denotes compounds with three hydrogen atoms formally associated with one sulfur atom; in the high-pressure literature it is often presented as the crystalline phase derived from the decomposition or rearrangement of hydrogen sulfide (H2S) or mixtures compressed in diamond anvil cells. Nomenclature varies: authors report H3S, the space-group-designated structural phases (e.g., Im-3m H3S), or assign systematic names in computational studies. The formula is central to discussions of phonon-mediated superconductivity, electronic structure, and quantum anharmonicity in dense hydrogen-rich materials studied by groups at institutions such as Max Planck Institute for Chemistry, Max Planck Institute for Solid State Research, Harvard University, and MIT.
At ambient conditions isolated H3S molecules are not stable; relevant descriptions concern periodic crystals where sulfur occupies lattice sites coordinated by hydrogen. The high-symmetry body-centered cubic Im-3m phase proposed for H3S contains sulfur atoms at body-centered positions with hydrogen in symmetric sites, producing short S–H bonds and a three-dimensional hydrogen sublattice. Electronic configuration analyses use projected density of states to show significant hybridization between sulfur 3p states and hydrogen 1s-derived bands near the Fermi level, yielding a high electronic density of states conducive to strong electron–phonon coupling. Studies often compare H3S to metallic hydrogen and other hydrides such as LaH10, highlighting similarities in charge transfer and band dispersion computed with density functional theory.
Quantum modeling of H3S relies on first-principles methods: density functional theory (DFT) for ground-state structure prediction, density functional perturbation theory (DFPT) for phonons, and Migdal–Eliashberg theory to estimate superconducting transition temperatures (Tc). Many groups have applied codes such as VASP, Quantum ESPRESSO, and WIEN2k with exchange–correlation functionals like Perdew–Burke–Ernzerhof (PBE) or hybrid functionals. Quantum Monte Carlo and anharmonic corrections via the stochastic self-consistent harmonic approximation (SSCHA) or path-integral molecular dynamics have been used to capture zero-point motion and nonadiabatic effects that modify phonon spectra and Tc. Key theoretical papers by researchers including Mikhail Eremets's collaborators, Dmitri A. Papaconstantopoulos, and Eugene Babaev framed computational protocols and benchmarks.
Vibrational spectroscopy of H3S phases under pressure is dominated by high-frequency S–H stretching modes and lower-frequency lattice phonons. Infrared and Raman active modes predicted for Im-3m H3S show strong S–H stretching peaks above 2000 cm−1 in calculations, but experimental observation is complicated by diamond anvil cell background and metallization. Anharmonicity and quantum zero-point energy substantially shift mode frequencies; these effects have been quantified using perturbative and nonperturbative approaches. Rotational spectra are not applicable to solid crystalline H3S phases; instead, lattice dynamics and phonon linewidths are reported and linked to electron–phonon matrix elements central to superconductivity. Experimental Raman studies have been conducted at facilities including European Synchrotron Radiation Facility and national high-pressure laboratories.
H3S attracted intense interest after theoretical predictions of superconductivity above 200 K in compressed hydrogen sulfide and subsequent experimental claims of high Tc in samples produced by compressing H2S or a mixture of H2 and S in a diamond anvil cell and annealing. The Im-3m phase of H3S is commonly cited as the superconducting phase observed near megabar pressures, with measured critical temperatures reported by groups led by Mikhail Eremets and corroborated by resistivity and magnetic susceptibility experiments. Phase diagrams show multiple pressure-induced transitions (molecular H2S → H3S and other hydrides like H4S3) and decomposition routes; theoretical convex-hull calculations and crystal structure prediction methods such as USPEX and CALYPSO were instrumental in mapping candidate phases. The mechanism is broadly described by conventional electron–phonon coupling within Eliashberg theory, though nonadiabatic and anharmonic corrections remain active research topics.
Under pressure H3S formation involves chemical reactions: dissociation of H2S, hydrogen diffusion, and recombination yielding hydrogen-rich solids. Isotopic substitution (e.g., deuterium to form D3S) provides critical tests of the phonon-mediated superconductivity mechanism via the isotope effect; reported isotope shifts in Tc support electron–phonon coupling but show anomalies indicative of anharmonicity. Chemistry at extreme conditions may produce related stoichiometries such as H5S2 or polymeric sulfur networks; computational thermodynamics and in situ spectroscopy track these transformations. Comparisons with other hydrides (e.g., YH6, LaH10) contextualize bonding motifs and superconducting trends across the periodic table.
Synthesis of H3S phases is typically achieved by compressing H2S gas or elemental sulfur with hydrogen in a diamond anvil cell to pressures of 100–200 GPa, often combined with laser or resistive heating to induce reaction and annealing. Characterization employs electrical transport measurements (four-probe resistivity), magnetic susceptibility, Raman and infrared spectroscopy, and synchrotron X-ray diffraction at facilities such as Diamond Light Source and Advanced Photon Source. Complementary isotopic experiments use deuterated gas. Challenges include sample containment, chemical purity, pressure calibration (ruby fluorescence or Raman edge), and disentangling signals from sample, gasket, and diamond; advanced cryogenic setups and microfabricated electrodes have improved data quality in recent experimental campaigns.
Category:Hydrogen compounds Category:High-pressure physics Category:Superconductivity