Hydrogen sulfides have recently received a great deal of interest due to the
record high superconducting temperatures of up to 203 K observed on strong
compression of dihydrogen sulfide (H2S). A joint theoretical and experimental
study is presented in which decomposition products and structures of compressed
H2S are characterized, and their superconducting properties are calculated. In
addition to the experimentally known H2S and H3S phases, our first-principles
structure searches have identified several energetically competitive
stoichiometries that have not been reported previously; H2S3, H3S2, and H4S3.
In particular, H4S3 is predicted to be thermodynamically stable within a large
pressure range of 25-113 GPa. High-pressure room-temperature X-ray diffraction
measurements confirm the presence of H3S and H4S3 through decomposition of H2S
that emerge at 27 GPa and coexist with residual H2S, at least up to the highest
pressure studied in our experiments of 140 GPa. Electron-phonon coupling
calculations show that H4S3 has a small Tc of below 2 K, and that H2S is mainly
responsible for the observed superconductivity of samples prepared at low
temperature (<100K).Y. L. and J. H. acknowledge funding from the National Natural Science Foundation of China under Grant No. 11204111 and No. 11404148, the Natural Science Foundation of Jiangsu province under Grant No. BK20130223, and the PAPD of Jiangsu Higher Education Institutions. Y. Z. and Y. M. acknowledge funding from the National Natural Science Foundation of China under Grant Nos. 11274136 and 11534003, the 2012 Changjiang Scholars Program of China. R. J. N. acknowledges financial support from the Engineering and Physical Sciences Research Council (EPSRC) of the U.K. [EP/J017639/1]. Calculations were performed on the Cambridge High Performance Computing Service facility and the HECToR and Archer facilities of the U.K.’s national highperformance computing service (for which access was obtained via the UKCP consortium [EP/K013564/1]). J. R. N. acknowledges financial support from the Cambridge Commonwealth Trust. I. E. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (FIS2013-48286-C2-2-P). M. C. acknowledges support from the Graphene Flagship and Agence nationale de la recherche (ANR), Grant No. ANR-13-IS10- 0003-01. Work at Carnegie was partially supported by EFree, an Energy Frontier Research Center funded by the DOE, Office of Science, Basic Energy Sciences under Award No. DE-SC-0001057 (salary support for H. L.). The infrastructure and facilities used at Carnegie were supported by NNSA Grant No. DE-NA-0002006, CDAC.This is the author accepted manuscript. The final version is available from the American Physical Society via http://dx.doi.org/10.1103/PhysRevB.93.02010