Phase Diagram and Symmetrization of Dense D2S

The phase diagram of D 2 S has been investigated to 70 GPa in diamond anvil cells using confocal micro-Raman spectroscopy. The results show that molecular phase IV transforms to “polymeric” phase V at 30 GPa at 300 K, analogous to an extended network structure of ice X with symmetrized hydrogen bonds. The formation of symmetrized phase V is evident by its characteristic single vibrational Raman peak at ∼460 cm –1 for symmetric D–S–D bending/stretching, analogous to that of ice X at ∼730 cm –1 at 76 GPa. At low temperatures, the proton-disordered phase IV transforms to more proton-ordered phases of IV′ and VI, which also transforms to phase V at 40 GPa at 100 K. The present phase diagram indicates that D 2 S is chemically stable at least to 70 GPa at 300 K, contrary to the previously reported decomposition to sulfur and H x S ( x > 2) above 30 GPa. This conclusion is important, considering that a wide range of decomposed states (H 3 S + S, H 3 S + + HS –, etc.) were used to explain the recently observed high T c superconductivity in dense H 2 S.