Structures of H2S:: Phases I′ and IV under high pressure

An x-ray-powder-diffraction experiment on solid H2S was performed with a diamond-anvil cell and an image plate to determine the unknown structures of phases I' and TV up to 25 GPa at room temperature. The structures of phases I' and IV were found to be cubic T-4-P2(1)3 and tetragonal D-4h(20)-I4(1)/acd, respectively, by the Rietveld method. Both structures were derived from an fee structure of phase I by slight atomic displacements of sulfur. Likely positions of hydrogen were examined by using the sulfur positions. Tn phase I', the H2S molecule had sixfold asymmetric coordination which brought the displacement from phase I. In phase TV, the molecules were found to form spiral chains along the c axis with partial loss of molecularity. The chains would be linked by hydrogen bonds.