The Crystal Sructure of Anthracene up to 22 GPa: a X-ray Diffraction Study
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The Crystal Sructure of Anthracene up to 22 GPa: a X-ray Diffraction Study Martin Oehzelt, Georg Heimel, Roland Resel Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria Peter Puschnig, Kerstin Hummer, Claudia Ambrosch-Draxl Institute for Theoretical Physics, Karl-Franzens-Universität Graz, Universitätsplatz 5, 8010 Graz, Austria Kenichi Takemura National Institute for Research Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan Atsuko Nakayama Research Center for Advanced Carbon Materials, National Institute of Advanced Industrial Science and Technology, Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan
ABSTRACT The aim of this study is to investigate the crystalline structure of anthracene C14H10 under high pressure performing angle dispersive x-ray diffraction experiments using synchrotron radiation in combination with Rietveld refinements and rigid body approximation. High hydrostatic pressure was applied up to 27.8 GPa using a diamond anvil cell. Full structural information (molecular orientations and lattice constants) is given up to a pressure of 20.3 GPa. At the highest pressure of 22.7 GPa the unit cell volume is decreased by 36.8%. Fourier transformation of the diffracted intensities reveals the electron density distribution within the unit cell. A pressure induced increase of the electron densities between adjacent molecules is observed. These findings are shown to be in agreement with theoretical calculations and hint towards the evolution of the anisotropic conductivity with pressure.
INTRODUCTION In the last decades, since the discovery of conducting polyacetylene, π-conjugated hydrocarbon materials have attracted a lot of attention. Impurities as well as chemical and structural defects in these materials often make a quantitatively correct modelling of the bulk properties impossible. Therefore small oligomeres of high purity have experienced a renewed interest. Especially the oligoacenes as small, rigid molecules, were often used as model molecules and show promising optical and electronic properties combined with high charge carrier mobilities.[1,2] The growth of single crystals of these molecules is well known [3] and high quality crystalline powder is commercially available. The long range order and chemical purity make the intrinsic physical properties easier accessible. Significant insight into the properties of these materials can often be gained by studying single molecules.[4] Especially their optical absorption and luminescence properties are dominated by single molecule effects. Nevertheless, for transport phenomena, the intermolecular interaction in terms of wavefunction overlap and low frequency (external) phonons play a crucial role.[5] Moreover, important optical features, such as the luminescence quantum yield in the solid state
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