Author: Michael Hanfland

Sixfold coordinated phosphorus by oxygen in AlPO4 quartz homeotype under high pressure.

2007

International audience; AlPO4 belongs to the berlinite quartz homeotype family, which has been the subject of intense high pressure research triggered by the supposed existence of reversible pressure induced amorphization. New x-ray diffraction experiments, complemented with ab initio calculations, demonstrate the existence of two high pressure crystalline polymorphs and show that AlPO4 share the same two stage densification mechanism as silica. In first place a compact hexagonal sublattice of oxygen atoms is formed. In a second step the cations redistribute in the interstices giving rise to a monoclinic distorted CaCl2 phase. The most outstanding feature of the new phase is that phosphorou…

DiffractionMaterials scienceInorganic chemistrychemistry.chemical_element02 engineering and technology010403 inorganic & nuclear chemistry01 natural sciencesOxygenAb initio quantum chemistry methodsStructural Biology0103 physical sciences[CHIM]Chemical SciencesGeneral Materials Science010306 general physicsQuartzBerliniteMechanical EngineeringPhosphorusGeneral ChemistryCondensed Matter Physics021001 nanoscience & nanotechnology0104 chemical sciencesCrystallographychemistryMechanics of MaterialsClose relationshipHigh pressure0210 nano-technologyMonoclinic crystal system

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Pressure-Induced Polymerization of Polycyclic Arene-Perfluoroarene Cocrystals: Single Crystal X-ray Diffraction Studies, Reaction Kinetics, and Desig…

2020

Pressure-induced polymerization of aromatic compounds leads to novel materials containing sp3 carbon-bonded networks. The choice of the molecular species and the control of their arrangement in the crystal structures via intermolecular interactions, such as the arene–perfluoroarene interaction, can enable the design of target polymers. We have investigated the crystal structure compression and pressure-induced polymerization reaction kinetics of two polycyclic 1:1 arene–perfluoroarene cocrystals, naphthalene/octafluoronaphthalene (NOFN) and anthracene/octafluoronaphthalene (AOFN), up to 25 and 30 GPa, respectively, using single-crystal synchrotron X-ray diffraction, infrared spectroscopy, a…

chemistry.chemical_classificationAnthraceneStackingInfrared spectroscopyGeneral ChemistryPolymerCrystal structure010402 general chemistry01 natural sciencesBiochemistryCatalysis0104 chemical scienceschemistry.chemical_compoundCrystallographyColloid and Surface ChemistryPressure-induced polymerization; single-crystal synchrotron X-ray diffraction; high-pressure kinetic studychemistryPolymerizationX-ray crystallographySingle crystal

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Effect of pressure on the structural properties and electronic band structure of GaSe

2007

The structural properties of GaSe have been investigated up to 38 GPa by monochromatic X-ray diffraction. The onset of the phase transition from the e-GaSe to a disordered NaCi-type structural motif is observed near 21 GPa. Using the experimentally determined lattice parameters of the layered e-phase as input, constrained ab-initio total energy calculations were performed in order to optimize the internal structural parameters at different pressures. The results obtained for the nearest-neighbor Ga-Se distance agree with those derived from recent EXAFS measurements. In addition, information is obtained on the changes of Ga-Ga and Se-Se bond lengths which were not accessible to a direct expe…

DiffractionBond lengthCrystallographyPhase transitionExtended X-ray absorption fine structureBand gapChemistryAb initio quantum chemistry methodsElectronic structureCondensed Matter PhysicsElectronic band structureMolecular physicsElectronic Optical and Magnetic Materialsphysica status solidi (b)

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