The 6th International Conference on Matter and Radiation at Extremes (ICMRE2023)

280 / 2023-04-25 01:34:36

PRESSURE-INDUCED SYNTHESIS AND PROPERTIES OF H2S-H2Se-H2 MOLECULAR ALLOY

high pressure,phase transition,Raman,structure,hydride

High Pressure Physics and Materials Science > Hydrogen and high-energy density material-poster

Since superconductivity found in H₃S with critical temperature as high as 203K, chalcogen hydrides have attracted extensive interest. Theoretical researches predict superconductivity on chalcogen hydrides under high pressure, for instance, H₃Se has critical temperature of 120K and H₄Te of 104K. However, selenium hydride is unstable under pressure and elemental decompose above 22 GPa at 300K. By heating S, Se and H₂, we synthesis a quenchable molecular alloy (H₂S_xSe_1-x)₂H₂. Density functional theory calculations predict that the alloy has substitutional disorder at room temperature, with any stoichiometry being possible. Comparing molecular dynamics (MD) calculations with Raman spectroscopic and X-ray diffraction experiments, we identify the symmetry of phase I is I₄/mcm with freely rotating. When further compressing above 20 GPa, constrained rotation of H₂S and H₂Se molecules indicates a transition to lower symmetry phase II. And it subsequently transforms to Cccm phase III where molecular rotation stops. The vibration Raman spectra disappear in phase III, indicative of hydrogen bond symmetry, while we observe band gap closure and increased reflectivity suggestive that the sample is metallic above 55 GPa.