First-principles study of crystal structures and superconductivity of ternary YSH6 and LaSH6 at high pressures

Abstract

We have performed a systematic study on the crystal structures and electronic properties of two ternary hydrides, YSH6 and LaSH6, under pressure, using the particle swarm optimization method and first-principles calculations. As a result of extensive structure searches, metallic YSH6 and LaSH6 are thermodynamically stable between 195-237 and 170-300 GPa, respectively. Interestingly, in YSH6 eight neighboring hydrogen atoms form octagons, and the octagons in different layers are connected by four sulfur atoms, forming a cagelike structure with a Y atom at the center, while those octagons in the same layer form polyphenylene-like chains via one shared side. In LaSH6, however, hydrogen atoms form both curved "H5" chains or straight chains when bonded to sulfur atoms. Furthermore, electron-phonon coupling calculations indicate that YSH6 and LaSH6 are promising superconductors with estimated Tc values of 91 and 35 K at 210 and 300 GPa, respectively. These results provide guidance for future experimental studies and stimulate more exploration on ternary hydrides.