title: Two high-pressure phases of SiS2 as missing links between the extremes of only edge-sharing and only corner-sharing tetrahedra.
abstract: The ambient pressure phase of silicon disulfide (NP-SiS2), published in 1935, is orthorhombic and contains chains of distorted, edge-sharing SiS4 tetrahedra. The first high pressure phase, HP3-SiS2, published in 1965 and quenchable to ambient conditions, is tetragonal and contains distorted corner-sharing SiS4 tetrahedra. Here, we report on the crystal structures of two monoclinic phases, HP1-SiS2 and HP2-SiS2, which can be considered as missing links between the orthorhombic and the tetragonal phase. Both monoclinic phases contain edge- as well as corner-sharing SiS4 tetrahedra. With increasing pressure, the volume contraction (-ΔV/V) and the density, compared to the orthorhombic NP-phase, increase from only edge-sharing tetrahedra to only corner-sharing tetrahedra. The lattice and the positional parameters of NP-SiS2, HP1-SiS2, HP2-SiS2, and HP3-SiS2 were derived in good agreement with the experimental data from group-subgroup relationships with the CaF2 structure as aristotype. In addition, the Raman spectra of SiS2 show that the most intense bands of the new phases HP1-SiS2 and HP2-SiS2 (408 and 404 cm(-1), respectively) lie between those of NP-SiS2 (434 cm(-1)) and HP3-SiS2 (324 cm(-1)). Density functional theory (DFT) calculations confirm these observations.
authors.affiliation: Department of Chemistry, Ludwig-Maximilian University of Munich , Butenandtstr. 5-13, D-81377 Munich, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Evers
authors.forename: Peter
authors.initials: P
authors.lastname: Mayer
authors.forename: Leonhard
authors.initials: L
authors.lastname: Möckl
authors.forename: Gilbert
authors.initials: G
authors.lastname: Oehlinger
authors.forename: Ralf
authors.initials: R
authors.lastname: Köppe
authors.forename: Hansgeorg
authors.initials: H
authors.lastname: Schnöckel