Emergent Magnéli-type crystal phases and their mixture in pressurized sulfur hydride

Abstract

Abstract The pressure-induced superconductivity in sulfur hydride has recently received tremendous amount of interest for its record-breaking transition temperature (Tc) of 203 K. We extensively discuss an infinite sequence of metastable structures of sulfur hydride under high pressure which has been recently proposed theoretically [R. Akashi et al., Phys. Rev. Lett. 117, 075503 (2016)]. The newly found structures are understood as the stacked layers of H2S and H3S, showing close similarity to the Magnéli phases formed in transition-metal oxides. The possible emergence of the “HxS Magnéli” phases are discussed as intermediate metastable phases in the formation of the high-Tc H3S phase. Superconducting transition temperatures and the Xray diffraction patterns are simulated with the first-principles calculations. It is demonstrated that the HxS Magnéli phases could serve as the silver bullet to explain the complicated dependences of the observed Tcs and diffraction patterns on the experimental protocol.