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

TY - JOUR

T1 - Crystal-structure properties and the molecular nature of hydrostatically compressed realgar

AU - Hejny, Clivia

AU - Sagl, Raffaela

AU - Többens, Daniel M.

AU - Miletich, Ronald

AU - Wildner, Manfred

AU - Nasdala, Lutz

AU - Ullrich, Angela

AU - Balic Zunic, Tonci

PY - 2012/5

Y1 - 2012/5

N2 - 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.

AB - 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.

KW - Realgar

KW - Diamond-anvil cell

KW - X-ray diffraction

KW - Density functional theory

KW - Absorption spectroscopy

KW - Raman spectroscopy

U2 - 10.1007/s00269-012-0495-y

DO - 10.1007/s00269-012-0495-y

M3 - Journal article

SN - 0342-1791

VL - 39

SP - 399

EP - 412

JO - Physics and Chemistry of Minerals

JF - Physics and Chemistry of Minerals

IS - 5

ER -