Single-crystal structure refinements and Debye temperatures of Ir₂S₃ kashinite and Rh₂S₃ bowieite

Single crystals of Ir₂S₃ (diiridium trisulfide) and Rh₂S₃ (dirhodium trisulfide) were grown in evacuated silica-glass tubes using a chemical transport method and their crystal structures were determined by single-crystal X-ray diffraction analysis. These compounds have a unique sesquisulfide structure in which pairs of face-sharing octahedra are linked into a three-dimensional structure by further edge- and vertex-sharing. Ir₂S₃ and Rh₂S₃ had similar unit-cell parameters and bond distances. The atomic displacement parameter (MSD: mean-square displacement) of each atom in Ir₂S₃ was considerably smaller than that in Rh₂S₃. The Debye temperatures (Θ_D) estimated from the observed MSDs for the Ir, S1 and S2 sites in Ir₂S₃ were 259, 576 and 546 K, respectively, and those for Rh, S1 and S2 in Rh₂S₃ were 337, 533 and 530 K, respectively. The bulk Debye temperature for Ir₂S₃ kashinite (576 K) was found to rank among the higher values reported for many known sulfides. The bulk Debye temperature for Rh₂S₃ bowieite (533 K) was lower than that for Ir₂S₃ kashinite, which crystallizes in the early sequences of mineral crystallization differentiation from the primitive magma in the Earth's mantle.