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  • 1
    Electronic Resource
    Electronic Resource
    A new analytic approximation to atomic incoherent X-ray scattering intensities (1975)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 31 (1975), S. 391-392 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A new analytic approximation to atomic incoherent X-ray scattering intensities is proposed. Unlike other approximations in the literature, the present function has the correct asymptotic behaviour at both large and small values of s. Fits to the incoherent intensities calculated by Cromer are presented for all atoms from He through Am.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S056773947500085X
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  • 2
    Electronic Resource
    Electronic Resource
    LALS: a linked-atom least-squares reciprocal-space refinement system incorporating stereochemical restraints to supplement sparse diffraction data (1978)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 34 (1978), S. 3-11 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: LALS is a computer program for the refinement of molecular structures. It is primarily intended for helical macromolecules but has applicability in other fields. The refinement uses as data, X-ray structure factors, usually from fibre diffraction studies, and/or stereochemical information, including a comprehensive short-contact search. Various other geometrical constraints and restraints may be placed on the molecular conformation. As parameters of the refinement, LALS uses primarily dihedral angles about single bonds, assuming bond lengths and angles to be fixed and known. This greatly reduces the number of parameters from conventional atom-position refinements, as is necessary in systems where data are sparse. LALS has been used successfully to investigate the structures of a large number of more or less ordered polynucleotides, polysaccharides and other fibrous materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739478000029
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  • 3
    Electronic Resource
    Electronic Resource
    Grain boundary structures in f.c.c. and b.c.c. metals and sites for segregated impurities (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 689-693 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The key features leading to low-energy grain boundaries in metals are discussed by reference to computer-simulated structures and geometrical analysis in terms of atom packing. Low energy is found to be associated with boundary structures consisting of relatively dense packing, and this can in turn be expressed in terms of the space-filling packing of coordination polyhedra. The geometrical method of analysis is shown to be well suited to the identification of interfacial sites for segregated impurities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739479001571
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  • 4
    Electronic Resource
    Electronic Resource
    The direct identification of stacking sequences in silicon carbide polytypes by high-resolution electron microscopy (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 916-923 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Lattice imaging with tilted illumination at the 2.5 Å level has been used for the direct determination of stacking sequences in silicon carbide polytypes by observation of electron micrographs. The method employed is first demonstrated by observations of the common short-period polytypes 3C, 4H, 15R and 6H, and is then used to reveal the stacking sequences in the polytypes 9R and 129R, neither of which appear to have been reported previously. Stacking sequences in disordered and faulted materials have also been characterised.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739479002059
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  • 5
    Electronic Resource
    Electronic Resource
    An estimate of crystallite size from the peak of the diffraction line-profile (1976)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 9 (1976), S. 139-141 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A simple method is proposed for determining the measure of crystallite size Dm = (\overline {D^4}/\overline {D^2})1/2 from the behaviour of a size-broadened line profile near its maximum. By comparison of this measure with that based on the integral breadth (DI = \overline {D^2}/\overline D), an indication is given of the width of the crystallite column length distribution in the material which avoids Fourier analysis. A procedure for removing the effect of the instrumental profile is developed, and the results applied to two supported metal catalysts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889876010765
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  • 6
    Electronic Resource
    Electronic Resource
    The reference intensity ratio, I/Ic, for computer simulated powder patterns (1976)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 9 (1976), S. 169-174 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A scale factor γ, to convert from the relative to the absolute/relative intensity scale, is readily calculated during computer simulation of powder patterns. Previously used scale factors are related to γ. The Reference Intensity Ratio, I/Ic (c = corundum), is obtained from μ, ρ, and γ for the sample and for corundum. Comparing calculated and experimental I/Ic values confirms that microabsorption and primary extinction can be serious experimental aberrations possibly limiting the accuracy to several wt.% in quantitative analysis by powder diffraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889876010807
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  • 7
    Electronic Resource
    Electronic Resource
    Automated computer indexing of powder patterns: the monoclinic case (1975)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 681-683 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A procedure for the computer indexing of powder diffraction patterns of monoclinic crystals is described. The method is based on locating the orthogonal hk0 and 0kl zones by means of two relationships among the Q (= 1/d2) values: 2Q020 + Qh10 = Qh30 and 3Q020 + Qh20 = Qh40. The monoclinic angle is determined by trying certain low-index h0l and hkl values for the reflections not already indexed and by determining if the entire pattern can then be indexed. A computer program has been written in Fortran IV and extensively tested on a variety of known patterns of various degrees of experimental accuracy and inherent difficulty. At present, about 60% of the test patterns can be indexed in an automated fashion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889875011600
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  • 8
    Electronic Resource
    Electronic Resource
    Crystallite shape and the Fourier analysis of diffraction line profiles (1976)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 9 (1976), S. 187-189 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The relation between the column distribution as determined from the Fourier analysis of diffraction line profiles and the overall size distribution is examined for mixtures of crystallites of uniform shape, but differing in size. It is concluded that for such systems Fourier analyses of a number of profiles can lead to information on the nature of the shape, but that very careful measurements will be necessary to generate useful information on the nature of the distribution of sizes. While the detailed application of the results of this model may be limited, more general consequences seem to be that (a) there is normally no superficial resemblance between the Fourier column distribution and the true size distribution and (b) information on the latter can only be extracted with difficulty from Fourier analyses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889876010923
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  • 9
    Electronic Resource
    Electronic Resource
    POWDER, an interactive computer system for neutron profile refinement (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 485-486 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A set of Fortran programs for the refinement of crystal structures using the Rietveld profile analysis technique have been written or adapted for use on an interactive computer. Facilities include distance and angle calculations, Fourier calculations and Madelung site energy calculations as well as the main refinement option.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889879013108
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  • 10
    Electronic Resource
    Electronic Resource
    Crystal data for ammonium thiosulphate (NH4)2S2O3 (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 246-246 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The current data listed in the powder diffraction file for ammonium thiosulphate are of poor quality. The compound crystallizes as thick tablets in a monoclinic cell, a = 10.224 (6), b = 6.500 (5), c = 8.802 (5) Å, β = 94.57 (5)°, Z = 4, space group C2/m. New indexed powder data are given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889879012280
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