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  • Al/Si orderingvacancy orderingceramicssuperspaceincommensurate structures  (1)
  • Allgemeine Physik  (1)
  • CHA zeolitescatalytic activitylocation of Cu2+synchrotron powder X-ray diffractionRietveld/maximum entropy method  (1)
  • EIGERhybrid pixel detectorselectron crystallographySAPO-34
  • International Union of Crystallography (IUCr)  (3)
  • American Institute of Physics (AIP)  (1)
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  • 1
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    Exploiting superspace to clarify vacancy and Al/Si ordering in mullite (2018)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publikationsdatum: 2018-06-26
    Beschreibung: Synchrotron single-crystal X-ray diffraction has revealed diffuse scattering alongside sharp satellite reflections for different samples of mullite (Al4+2xSi2−2xO10−x). Structural models have been developed in (3+1)-dimensional superspace that account for vacancy ordering and Al/Si ordering based on harmonic modulation functions. A constraint scheme is presented which explains the crystal-chemical relationships between the split sites of the average structure. The modulation amplitudes of the refinements differ significantly by a factor of ∼3, which is explained in terms of different degrees of ordering, i.e. vacancies follow the same ordering principle in all samples but to different extents. A new approach is applied for the first time to determine Al/Si ordering by combining density functional theory with the modulated volumes of the tetrahedra. The presence of Si–Si diclusters indicates that the mineral classification of mullite needs to be reviewed. A description of the crystal structure of mullite must consider both the chemical composition and the degree of ordering. This is of particular importance for applications such as advanced ceramics, because the physical properties depend on the intrinsic structure of mullite.
    Schlagwort(e): Al/Si orderingvacancy orderingceramicssuperspaceincommensurate structures
    Digitale ISSN: 2052-2525
    Thema: Geologie und Paläontologie , Physik
    Publiziert von International Union of Crystallography (IUCr)
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
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    Electron crystallography with the EIGER detector (2018)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publikationsdatum: 2018-02-15
    Beschreibung: Electron crystallography is a discipline that currently attracts much attention as method for inorganic, organic and macromolecular structure solution. EIGER, a direct-detection hybrid pixel detector developed at the Paul Scherrer Institut, Switzerland, has been tested for electron diffraction in a transmission electron microscope. EIGER features a pixel pitch of 75 × 75 µm2, frame rates up to 23 kHz and a dead time between frames as low as 3 µs. Cluster size and modulation transfer functions of the detector at 100, 200 and 300 keV electron energies are reported and the data quality is demonstrated by structure determination of a SAPO-34 zeotype from electron diffraction data.
    Schlagwort(e): EIGERhybrid pixel detectorselectron crystallographySAPO-34
    Digitale ISSN: 2052-2525
    Thema: Geologie und Paläontologie , Physik
    Publiziert von International Union of Crystallography (IUCr)
    Standort Signatur Erwartet Verfügbarkeit
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    AKTUELLE ARTIKEL
  • 3
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    Location of Cu2+ in CHA zeolite investigated by X-ray diffraction using the Rietveld/maximum entropy method (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publikationsdatum: 2014-11-12
    Beschreibung: Accurate structural models of reaction centres in zeolite catalysts are a prerequisite for mechanistic studies and further improvements to the catalytic performance. The Rietveld/maximum entropy method is applied to synchrotron powder X-ray diffraction data on fully dehydrated CHA-type zeolites with and without loading of catalytically active Cu2+ for the selective catalytic reduction of NOx with NH3. The method identifies the known Cu2+ sites in the six-membered ring and a not previously observed site in the eight-membered ring. The sum of the refined Cu occupancies for these two sites matches the chemical analysis and thus all the Cu is accounted for. It is furthermore shown that approximately 80% of the Cu2+ is located in the new 8-ring site for an industrially relevant CHA zeolite with Si/Al = 15.5 and Cu/Al = 0.45. Density functional theory calculations are used to corroborate the positions and identity of the two Cu sites, leading to the most complete structural description of dehydrated silicoaluminate CHA loaded with catalytically active Cu2+ cations.
    Schlagwort(e): CHA zeolitescatalytic activitylocation of Cu2+synchrotron powder X-ray diffractionRietveld/maximum entropy method
    Digitale ISSN: 2052-2525
    Thema: Geologie und Paläontologie , Physik
    Publiziert von International Union of Crystallography (IUCr)
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    AKTUELLE ARTIKEL
  • 4
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    Applied Physics Reviews
    American Institute of Physics (AIP)
    Online: 1(1).2014 –
    Details
    Verlag: American Institute of Physics (AIP)
    Digitale ISSN: 1931-9401
    Thema: Physik
    Schlagwort(e): Allgemeine Physik
    Standort Signatur Erwartet Verfügbarkeit
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