Superconducting H5S2 phase in sulfur-hydrogen system under high-pressure.

Takahiro Ishikawa,Katsuya Shimizu,Naoshi Suzuki,Akitaka Nakanishi,Hiroshi Katayama-Yoshida,Tatsuki Oda

doi:10.1038/srep23160

Takahiro Ishikawa, Katsuya Shimizu + Show 4 more

Open Access

https://doi.org/10.1038/srep23160

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Abstract

Recently, hydrogen sulfide was experimentally found to show the high superconducting critical temperature (Tc) under high-pressure. The superconducting Tc shows 30–70 K in pressure range of 100–170 GPa (low-Tc phase) and increases to 203 K, which sets a record for the highest Tc in all materials, for the samples annealed by heating it to room temperature at pressures above 150 GPa (high-Tc phase). Here we present a solid H5S2 phase predicted as the low-Tc phase by the application of the genetic algorithm technique for crystal structure searching and first-principles calculations to sulfur-hydrogen system under high-pressure. The H5S2 phase is thermodynamically stabilized at 110 GPa, in which asymmetric hydrogen bonds are formed between H2S and H3S molecules. Calculated Tc values show 50–70 K in pressure range of 100–150 GPa within the harmonic approximation, which can reproduce the experimentally observed low-Tc phase. These findings give a new aspect of the excellent superconductivity in compressed sulfur-hydrogen system.

Highlights

Hydrogen sulfide was experimentally found to show the high superconducting critical temperature (Tc) under high-pressure
We first explored stable structures of H5S2 by the genetic algorithm (GA) technique and first-principles calculations based on density functional theory (DFT), and compared formation enthalpy per atom among the obtained structures in pressure range from 50 to 250 GPa (Fig. 1)
The results show that H4S3 and H5S2 are below the line connecting between H3S and S but H4S3 is above the line connecting between H5S2 and S

Summary

Introduction

Hydrogen sulfide was experimentally found to show the high superconducting critical temperature (Tc) under high-pressure. Calculated Tc values show 50–70 K in pressure range of 100–150 GPa within the harmonic approximation, which can reproduce the experimentally observed low-Tc phase These findings give a new aspect of the excellent superconductivity in compressed sulfur-hydrogen system. High Tc superconductivity was experimentally observed in compressed hydrogen sulfide (H2S) and Tc reaches 203 K at 150 GPa2,3, which exceeds copper oxide superconductors[4,5] and sets a record for the highest Tc. In the experiments, the superconducting Tc shows 30–70 K in pressure range of 100–170 GPa for the H2S samples loaded at 100–150 K and compressed to 100 GPa (low-Tc phase) and increases to 203 K for the samples annealed by heating it to room temperature at pressures above 150 GPa (high-Tc phase). H5S2 takes a disorderly mixed structure of H2S and H2 molecules at 50 GPa, and it transforms into a monoclinic C2/m at 64 GPa and into a triclinic P1 with mixed H2S and H3S structure at 92 GPa

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