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  • 1
    Digitale Medien
    Digitale Medien
    Direct observation of tetrahedral hydrogen jumps in ice Ih (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 6801-6809 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Using deuteron NMR, spin alignment tetrahedral jumps of 2H in deuterated polycrystalline hexagonal ice (Ih) have been observed. Both geometry and time scale of the process are determined directly. At T=230 K the correlation time of these jumps is 0.21(3) ms. The tetrahedral hydrogen jumps turn out to scatter—most characteristically for the disorder within the hydrogen subsystem—randomly about the tetrahedral angles by about ±3° with a correlation time of 0.5(1) ms. With additional experiments on specifically doped ices it is shown that these tetrahedral jumps are due to diffusing Bjerrum vacancies.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.454426
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  • 2
    Digitale Medien
    Digitale Medien
    Neutron diffraction studies of ices III and IX on under-pressure and recovered samples (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 4878-4888 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Detailed structural studies using powder neutron diffraction have been carried out on ices III and IX on both under-pressure and recovered samples. The incomplete hydrogen ordering in recovered ice IX first observed by La Placa et al. is confirmed, and our studies suggest similar orderings for the under-pressure and recovered phases. Sample history was observed to influence the lattice constants of ice IX, an effect which could relate to hydrogen ordering. There is an indication that ice III is not fully disordered, a conclusion which would be consistent with independent thermodynamic measurements.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.464942
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  • 3
    Digitale Medien
    Digitale Medien
    The structure of the ice Ih by neutron diffraction (1983)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 87 (1983), S. 4312-4313 
    Details
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1021/j100244a063
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  • 4
    Digitale Medien
    Digitale Medien
    Lattice constants and thermal expansion of H2O and D2O ice Ih between 10 and 265 K (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 50 (1994), S. 644-648 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768194004933
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  • 5
    Digitale Medien
    Digitale Medien
    Electrocrystallization, crystal structure and physical properties of hexaperylene hexafluorophosphate, (C20H12)6.+.PF6− (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 50 (1994), S. 741-746 
    Details
    ISSN: 1600-5740
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108768194004027
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  • 6
    Digitale Medien
    Digitale Medien
    On the use of a small two-dimensional position-sensitive detector in neutron diffraction (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 562-568 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: A small position-sensitive 3He gas detector has been developed for diffraction studies using short-wavelength neutrons. It covers 32 × 32 pixels with a 2 mm resolution, which in the present set up corresponds to 0.25°, and the efficiency is 75% at a wavelength of 0.8 Å. The detector has been used for standard data collection, as well as for studies of twinned crystals and measurements involving parasitic reflections. In all cases it has improved the mode and speed of the measurement, with gain factors compared with single detectors which range from more than two in standard measurements to several hundred for the study of details of the Bragg peak(s). The computation time in data analysis and the storage of the data are no major limitations, partly due to the smallness of the data array, and partly due to efficient packing routines.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889889007752
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  • 7
    Digitale Medien
    Digitale Medien
    A closed-shell furnace for neutron single-crystal diffraction (1993)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 26 (1993), S. 730-733 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: The design and performance of a versatile closed furnace adapted to the needs of a neutron four-circle diffractometer with an offset φ axis are described. It operates between 300 and 1150 K with a long-term stability of typically 0.02 K and temperature gradients across the sample of less than 0.2 K cm−1. These numbers were established by calibration work at the α-incommensurable-β phase transitions in quartz. The furnace puts no restrictions on the access of reciprocal space. It is operated under high vacuum (typically 1̃0−3 Pa), with a water-cooled base. A flexible mantled thermocouple may be fixed directly on the sample. The maximum power needed at the highest temperature is approximately 50 W. Four thin-walled vanadium cans and a spherical aluminium can serve as heat shields and as vacuum confinement, respectively. The furnace has been in routine operation and has been used for a series of neutron single-crystal diffraction experiments in recent years.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889893004352
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  • 8
    Digitale Medien
    Digitale Medien
    Site-symmetry restrictions on thermal-motion-tensor coefficients up to rank 8 (1984)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 133-137 
    Details
    ISSN: 1600-5724
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: An extension of the tables for the site-symmetry restrictions on the thermal-motion-tensor coefficients to include tensors up to rank 6 (up to rank 8 for cubic, hexagonal, tetragonal and trigonal site symmetries) is presented. The dependence relationships of these symmetric polar tensors are calculated in their natural crystallographic lattice frames using a direct method.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108767384000295
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  • 9
    Digitale Medien
    Digitale Medien
    Statistical description of multimodal atomic probability densities (1983)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 148-158 
    Details
    ISSN: 1600-5724
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: A general method for describing multimodal atomic densities is presented. It is based on series expansions of a harmonic Gaussian probability density function. The most suitable expansion is of the Gram-Charlier type; its Fourier transform can be easily inserted in a structure factor equation. This statistical method yields a satisfactory fit to the data and allows for a better interpretation of the fit parameters than sophisticated split-atom models. The method is especially useful for weakly resolved modes and allows a better distinction between disorder and anharmonic motion than in conventional Fourier syntheses. Calculations on CsPbCl3, ice Ih and RbAg4I5 are presented to show the strengths and the limitations of this method.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108767383000240
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  • 10
    Digitale Medien
    Digitale Medien
    Generalized atomic displacements in crystallographic structure analysis (1992)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 48 (1992), S. 80-98 
    Details
    ISSN: 1600-5724
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: An attempt is made to summarize both theoretical and experimental aspects of generalized atomic displacement parameters (ADP's) in crystalline matter. Generalized displacement parameters are used to describe the weakening of Bragg intensities via the anharmonic (static or thermal) Debye–Waller factor (DWF) and its real-space counterpart, the generalized atomic probability density function (p.d.f.). The lattice dynamical base of the harmonic and anharmonic thermal DWF is discussed. It is pointed out that the static DWF frequently contains higher-order terms. The mathematical base for an experimental determination of generalized ADP's is given. The most popular current formulations (one-particle potential and statistical approaches) are reviewed and their individual limitations are discussed. Likewise the demands put on the quality and extent of experimental data are assessed. Some aids to the interpretation of generalized ADP's established by crystallographic least-squares procedures are given and a Monte-Carlo method for the calculation of errors in p.d.f. maps is presented. Finally, some prospects for future work are outlined and a more frequent comparison of theoretical calculations and experimental determinations of generalized ADP's is advocated.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108767391009510
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