Abstract
The discovery of superconductivity in H(3) S at 203 K marked an advance towards room-temperature superconductivity and demonstrated the potential of H-dominated compounds to possess a high critical temperature (T(c) ). There have been numerous reports of the H-S system over the last five years, but important questions remain unanswered. It is crucial to verify whether the T(c) was determined correctly for samples prepared from compressed H(2) S, since they are inevitably contaminated with H-depleted byproducts. Here, we prepare stoichiometric H(3) S by direct in situ synthesis from elemental S and excess H(2) . The Im 3‾ m phase of D(3) S samples exhibits a T(c) significantly higher than previously reported values (ca. 150 K), reaching a maximum T(c) of 166 K at 157 GPa. Furthermore, we confirm that the sharp decrease in T(c) below 150 GPa is accompanied by continuous rhombohedral structural distortions and demonstrate that the Cccm phase is non-metallic, with molecular H(2) units in the crystal structure.