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Träfflista för sökning "WFRF:(Kearley Gordon J.) "

Search: WFRF:(Kearley Gordon J.)

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1.
  • Lock, Nina, et al. (author)
  • Scrutinizing negative thermal expansion in MOF-5 by scattering techniques and ab initio calculations
  • 2013
  • In: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9234. ; 42:6, s. 1996-2007
  • Journal article (peer-reviewed)abstract
    • Complementary experimental techniques and ab initio calculations were used to determine the origin and nature of negative thermal expansion (NTE) in the archetype metal-organic framework MOF-5 (Zn4O(1,4-benzenedicarboxylate) (3)). The organic linker was probed by inelastic neutron scattering under vacuum and at a gas pressure of 175 bar to distinguish between the pressure and temperature responses of the framework motions, and the local structure of the metal centers was studied by X-ray absorption spectroscopy. Multi-temperature powder-and single-crystal X-ray and neutron diffraction was used to characterize the polymeric nature of the sample and to quantify NTE over the large temperature range 4-400 K. Ab initio calculations complement the experimental data with detailed information on vibrational motions in the framework and their correlations. A uniform and comprehensive picture of NTE in MOF-5 has been drawn, and we provide direct evidence that the main contributor to NTE is translational transverse motion of the aromatic ring, which can be dampened by applying a gas pressure to the sample. The linker motion is highly correlated rather than local in nature. The relative energies of different framework vibrations populated in MOF-5 are suggested by analysis of neutron diffraction data. We note that the lowest-energy motion is a librational motion of the aromatic ring which does not contribute to NTE. The libration is followed by transverse motion of the linker and the carboxylate group. These motions result in unit-cell contraction with increasing temperature.
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2.
  • Kearley, Gordon J., et al. (author)
  • Inelastic Neutron Scattering and Density Functional Theory- Molecular Dynamics Study of Si Dynamics in Ti3SiC2
  • 2014
  • In: Journal of the American Ceramic Society. - : Wiley. - 1551-2916 .- 0002-7820. ; 97:3, s. 916-922
  • Journal article (peer-reviewed)abstract
    • Observed differences between measured and calculated elastic constants for Ti3SiC2 are investigated using Density Functional Theory and Inelastic Neutron Scattering. The agreement between the calculated lattice dynamics and the dynamics measured by inelastic neutron scattering is considered good except at energies below similar to 20meV where discrepancies suggest anharmonic potentials. This suggestion is confirmed by Density Functional TheoryMolecular Dynamics simulation which shows multiple site occupancy of the Si atoms within the basal plane at finite temperature and produces a calculated inelastic spectrum in better agreement with the measured spectrum in the low-energy region. The highly anharmonic potential energy surface of the Si atoms offers an explanation for the failure of elastic constants, calculated based on the harmonic approximation, to agree with initial experimental measurements.
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