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  • 1975-1979  (13)
  • 1
    Electronic Resource
    Electronic Resource
    Diffraction by crystals with planar faults. II. Magnesium fluorogermanate (1976)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 32 (1976), S. 88-91 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Continuous streaks and the displacement of diffraction maxima from the perfect-crystal positions, observed in electron diffraction patterns of magnesium fluorogermanate suggest the existence of planar faults at which the c-axis dimension of the unit cell is contracted by 25%. High-resolution electron microscope images of thin crystals confirm this deduction. It is shown that even in the presence of strong dynamical-diffraction effects, electron diffraction patterns from thin crystals can be interpreted, within well defined limitations, by use of a kinematical theory such as is given in part I [Cowley (1976). Acta Cryst. A32, 83-87]. Using this kinematical theory calculations of diffraction intensity are made for reasonable assumptions of the form of the faults. The effect of the modification of the structure at the fault planes on the peak intensities is shown to be small so that structure analyses based on peak intensities only should give the structure of the unfaulted crystal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739476000168
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  • 2
    Electronic Resource
    Electronic Resource
    Electron microscopy study of ordering of potassium ions in cubic KSbO3 (1978)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 34 (1978), S. 625-634 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Ordered and disordered states of potassium ions in (111) tunnels in the structure of cubic KSbO3 have been studied by high-resolution electron microscopy. N-beam calculations for the images of both the ordered and disordered states reproduce well the observed images. The disordered state changes into the ordered state under electron irradiation during the observations. Electron diffraction from the specimens and optical diffraction from the images show diffuse spots due to small domains of the long-range-ordered state, but no other diffuse scattering due to short-range order has been observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739478001291
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Ewald dynamical diffraction symposium (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 1-1 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739479000012
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Dynamical theory for electron scattering from crystal defects and disorder (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 28-37 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Dynamical diffraction calculations have been made by use of the periodic-continuation assumption for the diffuse scattering in electron diffraction patterns and for electron microscope images of single split interstitials in gold crystals for thicknesses up to 200 Å in order to demonstrate the strong fluctuations of scattering with thickness. The diffuse scattering from distributions of defects in crystals, described in terms of correlation functions, can be written in terms of 'dynamical factors' for each type of individual defect. These dynamical factors multiply the same Fourier transforms of correlation functions as are used in kinematical theory to give the effect of dynamical scattering on the diffraction intensities. Calculations of dynamical factors have been made by multi-slice dynamical diffraction methods for unit changes in atomic scattering factors and for atom displacements in gold and aluminum crystals in [001] orientation for thicknesses up to 100 Å. With increasing thickness the dynamical factors show rapidly reducing fluctuations with crystal thickness and become more nearly isotropic except for the effects of Kikuchi bands which are seen to develop.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739479000061
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  • 5
    Electronic Resource
    Electronic Resource
    Diffraction by crystals with planar faults. I. General theory (1976)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 32 (1976), S. 83-87 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Kinematical diffraction from a crystal having planar faults is described by a systematic writing of the Patterson function and its Fourier transform for the general case of an arbitrary number of different kinds of layer, describing the faults in terms of a fault vector plus an addition, or subtraction, of scattering matter. The general series expression is readily simplified to deal with a wide variety of special cases. Particular examples include Wadsley-type shear faults associated with non-stoichiometry of oxides and the deformation and growth faults of simple close-packed structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739476000156
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  • 6
    Electronic Resource
    Electronic Resource
    Refinement of the defect structure of `GeNb9O25' by high-resolution electron microscopy (1976)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 32 (1976), S. 799-805 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: It has been previously established that calculations of intensity distributions in high-resolution electron-microscope images of crystal structures can reproduce the experimental observations. The use of comparisons Of observed and computed images for structure analysis has been extended for the first time to the refinement of a defect structure in the case of crystals of nominal composition 'GeNb9O25. The results show that previously proposed models for the disordered atom configurations around 'tetrahedral' sites are not completely correct. A new model is proposed which shows good agreement between computed and observed images. This model suggests an interpretation for observations on other related structures in terms of a new type of defect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739476001630
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Diffraction by crystals with planar faults. III. Structure analyses using microtwins (1978)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 34 (1978), S. 738-743 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The general theory for kinematical diffraction from crystals having planar faults is applied to the case of microtwinning and the related cases occurring in some minerals where there is a disordered sequence of two types of structure having small differences in composition, unit-cell dimensions and axial orientations. It is shown that, if intensities are measured for unresolved or partially resolved pairs of diffraction spots using conventional techniques, errors may well arise if the measurements are interpreted on the usual assumption that the intensities from the different crystal regions are summed incoherently. Calculations for representative cases suggest that errors, due to the neglect of the spreading of intensity maxima into continuous streaks, may amount to 20 or 30% when overlapping diffraction spots have structure amplitudes of opposite sign, but are usually much smaller, especially if the structure amplitudes are of the same sign.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739478001515
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  • 8
    Electronic Resource
    Electronic Resource
    Short-range ordering in PbMg1/3Nb2/3O3 (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 1015-1017 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: High-resolution electron-microscope images in conjunction with selected-area electron diffraction were used to investigate the short-range order in PbMg1/3Nb2/3O3. Intensity fluctuations of the [110] image indicated ordered domains extending over about 20 to 50 Å. Decomposition phases were observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739479002230
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  • 9
    Electronic Resource
    Electronic Resource
    Computed electron microscope images of atomic defects in f.c.c. metals (1978)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 34 (1978), S. 103-112 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The bright-field and dark-field electron microscope images expected for [100] split interstitials in thin crystals of gold and aluminum without and with lattice relaxation have been calculated by the method of periodic continuation including full n-beam dynamical interactions of both the Bragg reflections and the diffuse scattering. The advantage of using 1 MeV rather than 100 keV electrons is demonstrated in that, even with the same nominal resolution, the 1 MeV electrons give images in which the defect structure is more readily recognized. The conditions have been determined for which the defect images have high contrast and provide clear representations of the atom configurations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739478000182
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  • 10
    Electronic Resource
    Electronic Resource
    High-Resolution Electron Microscopy of Inorganic Materials (1976)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Materials Research 6 (1976), S. 53-81 
    Details
    ISSN: 0084-6600
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.ms.06.080176.000413
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