Crystal-structure properties and the molecular nature of hydrostatically compressed realgar

Clivia Hejny, Raffaela Sagl, Daniel M. Többens, Ronald Miletich, Manfred Wildner, Lutz Nasdala, Angela Ullrich, Tonci Balic Zunic

    12 Citationer (Scopus)

    Abstract

    The structure of realgar, As 4S 4, and its evolution with pressure have been investigated employing in situ X-ray diffraction, optical absorption and vibrational spectroscopy on single-crystal samples in diamond-anvil cells. Compression under true hydrostatic conditions up to 5.40 GPa reveals equation-of-state parameters of V 0 = 799.4(2.4) Å 3 and K 0 = 10.5(0.4) GPa with = K′ 08.7. The remarkably high compressibility can be attributed to a denser packing of the As 4S 4 molecules with shortening of the intermolecular bonds of up to 12 %, while the As 4S 4 molecules remain intact showing rigid-unit behaviour. From ambient pressure to 4.5 GPa, Raman spectra exhibit a strong blue shift of the Raman bands of the lattice-phonon regime of 24 cm -1, whereas frequencies from intramolecular As-S stretching modes show negligible or no shifts at all. On pressurisation, realgar shows a continuous and reversible colour change from bright orange over deep red to black. Optical absorption spectroscopy shows a shift of the absorption edge from 2.30 to 1.81 eV up to 4.5 GPa, and DFT calculations show a corresponding reduction in the band gap. Synchrotron-based measurements on polycrystalline samples up to 45.5 GPa are indexed according to the monoclinic structure of realgar.

    OriginalsprogEngelsk
    TidsskriftPhysics and Chemistry of Minerals
    Vol/bind39
    Udgave nummer5
    Sider (fra-til)399-412
    Antal sider14
    ISSN0342-1791
    DOI
    StatusUdgivet - maj 2012

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