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  • International Union of Crystallography (IUCr)
  • PANGAEA
  • 1980-1984  (6,613)
  • 1960-1964  (1,878)
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  • 1
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 307-310 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Transparent yellow-greenish single crystals of Pb6GeO8 were obtained by spontaneous crystallization from a melt with a molar ratio of PbO:GeO2 = 4.7:1. The compound is monoclinic, probable space group P21/a, a = 52.665 (12), b = 15.063 (4), c = 23.949 (6) Å and β = 111.03 (5)°; Dm(293 K) = 8.65 (3), Dx = 8.653 Mg m−3 for Z = 64 formula units. Pb11Ge3O17 was synthesized by sintering high-purity oxides PbO and GeO2 of molar ratio 3.69:1 at 990 K. The compound is also monoclinic, probable space groups C2/c or Cc, a = 25.117 (5), b = 15.440 (2), c = 45.529 (13) Å and β = 103.20 (4)°; Dm(293 K) = 8.55 (2), Dx = 8.560 Mg m−3 for Z = 32.
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  • 2
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 311-315 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Series of chalcopyrite-type solid solutions AgGaxIn1−xSe2 and CuGaxIn1−xSe2, 0≤x≤1, have been prepared by direct synthesis from the melt. The space group is I\bar 42d (No. 122), Z = 4. The unit-cell parameters a and c and the ratio c/a change linearly with x. Powder data at 298 K are given for AgGaSe2, AgGa0.80In0.20Se2, AgGa0.70In0.30Se2, AgGa0.40In0.60Se2, AgGa0.20In0.80Se2 and AgInSe2, and for CuGaSe2, CuGa0.60In0.40Se2, CuGa0.30In0.70Se2 and CuInSe2.
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  • 3
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 318-337 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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  • 4
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 338-339 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: If the length of the focal spot is increased while the width remains constant, X-ray output can be increased without changing the specific loading on the anode.
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  • 5
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 391-394 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: To increase the integrated reflexion intensity of a monochromating crystal, the strain distributed due to impurity introduction can be utilized and, compared with conventional mechanical processing, can be a more controllable method. From this viewpoint, numerical computations on the dynamical diffraction theory for distorted crystals have been performed for the 220 reflexion of Cu Kα X-rays by Si crystals with several different strain distributions; the one changing linearly with depth from −10−3 at the surface to zero at 28 μm depth gives the maximum integrated intensity within the restriction that the full width of the intensity profile is 100′′. The integrated intensity in this case is 5.3 and 4.5 times as strong as that of a perfect crystal plate for σ and π polarizations respectively. It is more enhanced for shorter wavelengths, e.g. nine times for Mo Kα. In addition, that intensity profiles for distributed strains are cut sharply at both ends is certainly favourable for the purpose of monochromating white X-rays. A preliminary experiment with an intentionally processed sample showed a fourfold intensity increase for a σ-polarized Cu Kα line with a full width of 80′′.
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  • 6
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 401-401 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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  • 7
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 88-92 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The device described here has been designed to perform microcreep experiments and, simultaneously, to get X-ray topographic images of the sample. Such dynamic experiments are now possible with white synchrotron radiation (LURE-DCI Orsay). The sample material, germanium, is hard to machine; so a simple shape was chosen (rectangular platelet 20 × 5 × 0–2 mm). The grip system is quite simple and the whole assembly is compact enough to be adapted to fit a standard goniometer head. Temperatures as high as 923 K in air and forces up to few tens of Newtons can be reached. The first experiments on Ge bicrystals have shown the device to perform as expected.
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  • 8
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 78-87 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A polished plate of type Ia natural diamond, containing regions which had been bombarded by electrons of energy between 2.0 and 4.5 GeV to total doses of 1̃024 electrons m−2 in polarized-photon production experiments, was examined, both before and after annealing at 1133 K for 8 h, using birefringence, cathodoluminescence photography and spectroscopy, X-ray topography and a novel method for mapping differences of interplanar spacing; `dilatation topography'. The annealing effected some reduction of overall strain, but it also generated an enhancement of diffraction contrast and cathodoluminescence at certain grown-in defects that the specimen contained. By means of dilatation topographs, interplanar spacings in a region of maximum electron-beam damage were compared with those in least-damaged regions some millimetres away. In the case of (110) planes that had been grazed by the electron beam, the maximum relative expansion, Δd/d, in damaged regions so found was reduced from 1.2 × 10−3 to 0.9 × 10−3 by the annealing. Evidence was obtained that the magnitude of expansion in the region of maximum damage was dependent upon crystallographic direction. Criteria are suggested for selection of diamonds to be used in polarized-photon production experiments.
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  • 9
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 93-95 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Cell data for monoclinic sebacic acid COOH(CH2)8COOH, C10H18O4, and dodecanedioic acid COOH(CH2)10COOH, C12 H22O4, are accurately given: (C10) a = 15.064 (6), b = 4.987 (4), c = 10.142 (6) Å, β = 133.14 (5)°; (C12) a = 17.594 (8), b = 4.933 (3), c = 10.174 (5) Å, β = 132.35 (3)°. It is shown that crystallographic data for molecular alloys [C10]x[C12]1 −x are significantly different for those prepared by fusion (m.a.f.) and those by sublimation (m.a.s.). X-ray powder data are given for the two series of solid solutions.
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  • 10
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 95-96 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The cell constants for the title compound, HMTSFT–CNQ4, (C12F4N4).(C12H12Se4), M.W. 748.21, were determined from a single crystal exposed on a Syntex P{\bar 1} automated diffractometer and then refined from precision powder data with Cr Kα1 (2.28962 Å): a = 21.906 (5), b = 12.918 (3), c = 4.0184 (10) Å and β = 91.658 (10)°; U = 1136.7 Å3, Z = 2, space group C2/m; Dc = 2.186 Mg m−3.
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  • 11
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 128-131 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A &psgr;-φ goniometer with two axes of rotation, driven by stepping motors, was designed as an attachment for a horizontal &thgr;/2&thgr; goniometer. By means of this arrangement it is possible to measure strains and compute stresses in single crystals and in separate crystals of a bicrystal or a coarse-grained polycrystalline specimen. The available rotations also make it possible to investigate residual macrostresses and textures in polycrystalline specimens. Results of the test measurements on a tensile specimen of a molybdenum single-crystal are given.
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  • 12
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 132-134 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A calculation of γ(r), the correlation function which gives the X-ray scattering of a cubic object of uniform density, is given for the full range of r. A new method, which can be applied to other systems, is used. The function γ(r) and its first derivative are everywhere continuous, but γ′′(r) is discontinuous at r = L and r = L□2 (L = cube edge length). This leads to an intersect distribution of unexpected shape. The scattering intensity as a function of angle is calculated by Fourier inversion of γ(r).
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  • 13
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 135-140 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An experimental method is described which enables the inelastically scattered X-ray component to be removed from diffractometer data prior to radial density function analysis. At each scattering angle an energy spectrum is generated from a Si(Li) detector combined with a multi-channel analyser from which the coherently scattered component is separated. The data obtained from organic polymers has an improved signal/noise ratio at high values of scattering angle, and a commensurate enhancement of resolution of the RDF at low r is demonstrated for the case of PMMA (ICI `Perspex'). The method obviates the need for the complicated correction for multiple scattering.
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  • 14
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 148-153 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Until now, the calculation of intensities diffracted by layer structures has only been treated in the two extreme cases, namely (i) the layers interfere completely and (ii) the layers do not interfere (turbostratic structures). The present paper develops the mathematical treatment which allows the calculation in the intermediate case, namely when layers are only partially interfering.
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  • 15
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 141-147 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A niobium tungsten bronze crystal with a nominal composition 3 Nb2O5.8WO3 gives circular diffuse scattering in the electron diffraction pattern. The diffuse rings change shape and size when the crystal is reduced at high temperature. The observations are explained by improving the cluster model proposed by De Ridder, Van Tendeloo, Van Dyck & Amelinckx [Phys. Status Solidi A (1977), 41, 555–560]; the present clusters are composed of nine pentagonal-tunnel sites. The 1 MV high-resolution electron microscope images reveal that the clusters have several different atomic arrangements and compositions. The relation between the clusters and the micro-domains, formed in the initial stage of long-range ordering, is clarified.
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  • 16
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 163-167 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Analysis of Bragg X-ray intensities collected on a single-crystal diffractometer with a pyrolitic graphite monochromator in the diffracted beam has revealed small systematic errors which are a consequence of the necessarily large illuminated area of monochromator crystal.
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  • 17
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 154-162 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The amount of information which can be obtained from a small-angle X-ray experiment can be considerably increased by orienting the solute particles with external forces during the scattering experiment. In this paper it is shown that orientation by flow, for instance through a capillary tube, gives additional information about size, shape, flexibility and rotational diffusion of the particles. The only requirement, in order to obtain flow-oriented samples, is that the solute particles must be relatively large and asymmetric. On the other hand, if the scattering curve is dependent on the flow rate through the capillary, it can immediately be concluded that the solute particles are asymmetric (or they are deformed in the hydrodynamic field). Equations describing the relationship between flow rate, molecular shape and scattered intensity are given, and theoretical intensity patterns for some representative cases are presented. It follows that there is a fundamental difference in scattering patterns for oblate and prolate ellipsoids of revolution. This difference can be used to differentiate between these two cases. Some experimental results obtained using inorganic model colloids are presented.
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  • 18
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 168-175 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An analysis of the small-angle scattering problem based on Shannon sampling is presented. It is shown that this approach leads to an accurate assessment of the information contained in a given data set and rigorous estimates of the errors inherent in the parameters derived therefrom.
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  • 19
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 3-7 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: There has recently been an increased amount of interest in laboratory equipment for extended X-ray absorption fine-structure (EXAFS) measurements. In an earlier paper a facility for performing such measurements easily in a few hours was described in some detail. In this paper, further development of the techniques is reported. The use of high-power rotating-anode X-ray generator, the design of an X-ray curved-crystal spectrometer, the factors governing the proper choice of monochromator crystals and the design of fast-counting detectors and electronics are discussed. In addition, it is shown how errors caused by characteristic lines in the spectrum can be eliminated by use of a flux stabilization circuit.
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  • 20
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 24-27 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Photographic neutron intensity measurements on a 2 mm3 single-crystal of triclinic lysozyme are compared with conventional neutron diffractometer data. The reflections were recorded with the oscillation technique. The structure factors were derived from the optical densities scanned by an automatic microdensitometer and processed by computer programs. A statistical analysis shows that the photographic data are of about the same accuracy as recently collected diffractometer data. For the same flux and crystal volume the data collection time is reduced by up to two orders of magnitude.
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  • 21
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 43-50 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A device is described which uses liquid nitrogen to generate a cold or hot gas stream which is blown directly onto the crystal mounted on an X-ray diffractometer. With a specially constructed high-vacuum (〈 1.3 × 10–5 Pa) jacketed silica Dewar tube, it can operate between 83 and 1120 K with a stability over long time periods of ± ¼ K below and ± 1 K above ambient temperature. In the latter case the short-time stability is ± ¼ K for hours. It gives an inert atmosphere at elevated temperatures and allows extensive data collection for the accurate determination of crystal structures. The evaporator, the automatic refilling system and the silica Dewar tube are described.
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  • 22
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 60-61 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A fitting method is proposed for X-ray diffraction profiles which requires only a small number of parameters.
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  • 23
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 61-62 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Complete solid solution is observed amongst the compounds of the type M1MgCr2(VO4)3 (where M1 = K, Rb or Tl). The solid-solution series obtained show linear changes in peak positions and peak intensities in their X-ray diffraction patterns. The crystallographic behaviour with respect to the value of x for (RbxK1−xMgCr2(VO4)3 and (TlxK1−x)MgCr2(VO4)3 solid solutions is discussed.
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  • 24
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 64-65 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Indexed powder patterns of the monoclinic phase, stable at room temperature, and of the orthorhombic phase, stable for T 〉 786 K, are given. The cell dimensions are: a = 15.737 (8), b = 9.231 (5), c = 18.224 (9) Å, β = 125.46 (2)° at 295 K; a = 9.330 (3), b = 12.868 (5), c = 9.242 (3) Å at 818.6 K. Linear equations describing the thermal expansion of the two phases of ferric molybdate are reported. To verify if ferric molybdate can incorporate excess MoO3, measurements on non-stoichiometric samples were also made: no evidence of the presence of excess MoO3 was found.
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  • 25
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 68-68 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: High-temperature As2O5 at 768 ± 5 K is tetragonal with a = 8.577 (1), c = 4.637 (1) Å, V = 341.2 Å3, Z = 4, Dc = 4.475 Mg m−3. Indexed powder data are given.
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  • 26
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 85-93 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A flat, relatively thin (9 mm) xenon-filled multiwire proportional counter with two-dimensional, 2 μs delay line readout of a 270 × 300 mm active area has been developed for use as a position-sensitive area X-ray detector in the 8 keV energy region (Cu Kα) used in crystallographic structure work with large biological molecules. Its quantum detection efficiency for 8 keV X-ray photons is about 0.5, a value which is spatially uniform to within ± 2%. Its dead-time loss fraction at a typical data collection rate of 30000 photons s−1 is 12%. The detector has spatial resolution for X-rays of 0.6 mm FWHM in the horizontal direction and 2 mm, the anode wire spacing, in the vertical direction. The effects of parallax are found to be limited and do not seriously increase the apparent size of the diffracted beams. The position sensitivity of this detector is geometrically linear to within 0.5 mm across its active surface. Routine maintenance of the detector requires the attention of a skilled technician but is not time consuming. For four years, this detector has been used to measure millions of reflection intensities from crystals of many different proteins. The down time due to the detector has averaged less than four days per year, considerably less than the down time of other components of the data collection system. Four new protein structures have now been solved using data from this detector. Also, a considerable amount of data have been collected at higher resolution or at different temperatures with crystals of other proteins.
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  • 27
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 124-130 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The sources of systematic error in the X-ray diffractometer method of stress measurement are discussed. The errors in stress measurement and correction procedures for their elimination are described and quantitatively assessed.
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  • 28
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    Applied crystallography online 14 (1981), S. 117-123 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The diffraction aspect and rough cell parameters of a crystal to be studied are usually known before mounting the crystal on a diffractometer. Such data are used for orientation purposes in the method described. An ordered list of indexed 2θ values is calculated from which an optimum 2θ for a peak search is derived. The peaks found are centered, their possible unique indices are derived by comparison of the observed 2θ values with the calculated values. Two intense reflections with few indexing ambiguities are selected to define the crystal orientation. Their possible pairs of indices are found by considering combinations of indices related to the unique indices by the Laue-group symmetry and for which the calculated angle between the reciprocal vectors is comparable with the observed angle. Only the non-equivalent orientations defined by these initial pairs will be accepted. An initial pair will be rejected if the indices of both reflections can be transformed into those of a previously accepted pair by a single Laue-group symmetry operator of the first kind. The correct setting is usually obvious from a very short list of possible orientations and is retained. This simple approach has been programmed and treats all symmetries without branching of the logic. Rhombohedral crystals can be referred to hR or rP cells. The possible non-equivalent settings due to metric ambiguities, to pseudo-symmetry or to symmetry are exhaustively listed, but no symmetry-related setting is indicated. This scheme has automatically oriented more than 40 crystals from the seven crystal systems in 20–50 min each. The wavelength, the cell parameters and the short symbol of a valid space group in the correct diffraction aspect are the only input.
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  • 29
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 137-139 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Neutron time-of-flight powder data have been collected for forsterite [Mg2SiO4; Pbnm (D162h, No. 62); Z = 4, a = 4.7534 (1), b = 10.1989 (2), c = 5.9813 (1) Å] with the ZING-P′ high-resolution diffractometer at Argonne National Laboratory. Forty-seven variables, including anisotropic temperature-factor coefficients, were refined with a profile-fitting procedure to R(profile) = 2.10% and R(Rietveld) = 3.53%. Positional and thermal parameters are in good agreement with those determined from recent X-ray and neutron single-crystal diffraction experiments. Results suggest that powder data can be used to obtain accurate positional parameters and reasonable temperature factors for moderately complex structures.
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  • 30
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 139-141 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A Kratky small-angle X-ray camera was modified so as to allow the use of a one-dimensional (one-dimensional) position-sensitive detector (PSD) with it. The modification was designed in such a way that most of the calibrations, necessary for subsequent correction of the collected intensity data, can be performed with little alteration in the collimation geometry or the electronics settings. In particular, the calibration of the uniformity of detector efficiency can be performed by repeated vertical travel of the detector at a constant speed across a beam scattered from a sample.
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  • 31
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    Applied crystallography online 14 (1981), S. 145-148 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A computer program for the separation of a composite peak into the components and the background has been written in Fortran. Each component is approximated by a function of the form y(x) = c [1 + ({{x - d}\over{e}})^{2}]^{-f}, where c, d, e and f are the parameters to be determined by a least-squares method. Arbitrary, known or assumed relations among the parameters of different components may be read in to reduce the number of independent parameters and save computation time or, in other cases, to offer a better chance of separating a complex composite peak by varying a subset of the parameters.
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  • 32
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    Applied crystallography online 14 (1981), S. 151-153 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A computer program has been written with the aim of calculating the domain of an atom in a structure. The domain may be limited by planes situated half-way between the atoms, or at a distance that takes into account the relative radii of the atoms. Data concerning this domain and the corresponding coordination polyhedron are computed and printed. Punched cards, to be used in a special plotting program, can also be produced. Three types of weighted coordination number are calculated.
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  • 33
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    Applied crystallography online 14 (1981), S. 160-168 
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    Notes: Intensity can often be measured as a continuous function of scattering angle in diffraction from non-crystalline specimens. An analysis of the amount of information contained in one-dimensional continuous diffraction data is presented here. This analysis, based on the sampling theorem and the theory of entire functions, indicates that there is a limited but often rather large number of possible phase solutions to any given continuous intensity distribution. A refinement technique has been developed which allows phase solutions to be found that are consistent with the diffraction data and with other physical and chemical data. In favourable cases, when diffraction data is used in coordination with other kinds of data, there can be enough information in a diffraction pattern to identify a unique structural solution.
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  • 34
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    Applied crystallography online 13 (1980), S. 401-402 
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  • 35
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    Applied crystallography online 14 (1981), S. 370-382 
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    Notes: A small-angle neutron scattering (SANS) spectrometer has been constructed at the University of Missouri Research Reactor Facility (MURR). The design of the MURR–SANS is unusual in that the size of the reactor containment building constrains the flight path to be vertical. This is achieved by Bragg scattering upward through 90° from a set of slightly misaligned pyrolytic graphite crystals to provide a neutron beam at 4.75 Å with a wavelength spread of approximately 4.1%. The beam incident on the sample is defined by two matched variable apertures located either 3.0 or 4.5 m apart. The evacuated scattered flight path is designed with removable extensions to match the primary flight path in length. The instrument has an automatic sample handling capability provided by its own dedicated PDP 11/03 computer. The detector is a large assembly of commercially available linear 3He detectors as an economic alternative to a crossed-wire two-dimensional multi-detector. An array of 43 position-sensitive proportional counters, 24 in (609.6 mm) long and 0.5 in (12.7 mm) in diameter, using charge division gives a spatial resolution of 5 x 12.7 mm. The area-averaged detector efficiency is about 84% at a wavelength of 4.75 Å. The range of scattering vectors that can be measured is 0.005 〈 Q〈 0.15 Å−1. The instrument is well suited to a wide variety of experiments on specimens having characteristic dimensions between 20 and 500 Å. MURR–SANS is designed as a user-oriented facility which provides both reasonable resolution and intensity on sample at a modest cost, and forms part of a neutron scattering center.
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  • 36
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    Notes: Two-dimensional antiphase domain structures existing in the composition range 20–23 at.% Mn were investigated by a high-resolution structure-imaging technique with a 1 MV electron microscope. The structures are based on the DO22 structure and consist of parallelogram-shaped domains containing 4 × 3 columns of Mn atoms and lozenge-shaped domains with 4 × 4 and 3 × 3 columns, and the domains are separated by two-dimensional antiphase boundaries parallel to the ({\bar 2}40) and (240) planes of the fundamental face-centred structure. The configuration of the domains changes delicately with a slight change of composition or annealing temperature, and the symmetry of the structure is lowered below about 670 K. The ideal structure models have compositions of about 22.7 at.% Mn. The images of about half of the specimen area of the 22.6 at.% Mn alloy annealed at 570 K do not correspond to these new structures, but bear a resemblance to the image expected from the two-dimensional antiphase structure proposed by Watanabe [J. Phys. Soc. Jpn (1960), 15, 1030–1040] for Au3Mn, which is based on the L12 structure and has boundaries parallel to the (100) and (010) planes.
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  • 37
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    Applied crystallography online 14 (1981), S. 432-436 
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    Notes: Two methods for the numerical resolution of the Takagi-Taupin equations are compared. It is shown that for a small integration step Taupin's [Acta Cryst. (1967), 23, 25–35] extension to two dimensions of the one-dimensional Runge–Kutta third-order method is more accurate than the algorithm of Authier, Malgrange & Tournarie [Acta Cryst. (1968), A24, 126–136] but, for a given precision, Authier, Malgrange & Tournarie's method is faster than Taupin's so the former will usually be preferred for numerical calculation.
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  • 38
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    Applied crystallography online 14 (1981), S. 444-446 
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    Notes: The phase separation of an 80% B2O3–15% PbO–5% Al2O3 (weight %) glass after splat-cooling was studied by small-angle X-ray scattering. The wavenumber which receives maximal amplification and the scattering intensity corresponding to this wavenumber were determined as a function of the cooling rate of the glass. The experimental results qualitatively agree with the main features of previous calculations based on the linear theory of spinodal decomposition, but no quantitative agreement is obtained.
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  • 39
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    Applied crystallography online 14 (1981), S. 455-461 
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    Notes: An analysis of published X-ray diffraction data from nerve myelin is given based on the properties of analytic functions. Functions defined by a finite Fourier transform may be described by their distribution of zeros. This description allows a phase function to be determined from real data, which is unique in principle. A solution to the phase assignment is given and compared with corresponding published solutions derived by other methods. The strong measure of agreement for the phases of the first nine diffraction orders, and the stability of this agreement against the efforts of experimental error, leads to the conclusion that these phases are probably correct.
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  • 40
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    Applied crystallography online 14 (1981), S. 465-465 
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    Notes: The powder data for [2.1.2.1]paracyclophan is reported. This compound is monoclinic with a = 21.44 (4), b = 17.22 (6), c = 9.70 (4) Å, γ = 141.30 (3)°, Z = 4.
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    Applied crystallography online 14 (1981), S. 491-491 
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  • 42
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    Applied crystallography online 15 (1982), S. 5-14 
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    Notes: A method of measuring accurate cubic lattice parameters is developed which is suited to the type of conditions encountered in high- and low-temperature powder diffractometry. This is based on the fact that the absolute Bragg angle of each line in an indexed cubic diffraction pattern can be determined from a knowledge of the differences in angles between lines. Accurate zero-angle alignment, therefore, is unnecessary. Furthermore, it is shown that the peak or centroid shift of the line profiles arising from the instrumental and physical aberrations can be determined directly from the measured angular data without assuming a specific angular dependence. In practice the accuracy of the method is of the order of 0.0002 Å for a lattice parameter of approximately 8 Å.
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  • 43
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    Applied crystallography online 15 (1982), S. 20-26 
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    Notes: Calculations of diffraction line profiles and Scherrer constants for crystallites whose external shape has cubic symmetry are extended to crystallites of cylindrical shape. The analysis includes the limiting cases of acicular crystals and disks and, to a reasonable degree of approximation in many cases, to hexagonal prisms. These shapes have applications in size determination for materials which form prismatic crystallites, particularly those which belong to the hexagonal system or have been derived from substances with this symmetry.
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    Applied crystallography online 15 (1982), S. 35-38 
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    Notes: The Warren–Averbach profile analysis was modified to study the deformed state of Al. The X-ray diffraction effect of dislocations locating on cell boundaries may be treated as `size broadening', while that of dislocations inside cells is `strain broadening', which may be treated with Wilkens's theory. X-ray Debye profile measurement was performed on deformed, recovered and annealed samples of commercial pure Al. Some information concerning the dislocation glide systems and distribution as well as the differences between the deformed and recovered state were given by the Debye profile analysis. The results are in good agreement with those obtained by other authors, which prove the reliability and correctness of the method.
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    Applied crystallography online 15 (1982), S. 39-47 
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    Notes: The extended structure of the Pt L3 X-ray absorption edge for some platinum compounds was measured and Fourier inverted. It is shown that the way in which the contribution of the isolated atom is subtracted from the absorption spectrum may influence the shape of the first peak in the Fourier transform and possibly lead to erroneous structural interpretations concerning the first-neighbour shell of the absorbing atom. These errors are the more important the smaller the separation between the absorbing atom and its nearest neighbours. An improved method of subtraction of the isolated-atom absorption is proposed and checked.
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  • 46
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    Applied crystallography online 13 (1980), S. 605-607 
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    Notes: The crystal structure of Ta5P3 has been refined from Guinier–Hägg X-ray powder film data [Malmros & Thomas (1977). J. Appl. Cryst. 10, 7–11] using positional parameters from its structural isomorph Nb5P3 as starting values. The space group is orthorhombic Pnma (No. 62), with refined cell parameters a = 25.3210 (4), b = 3.4013 (1), c = 11.4614 (2) Å, V = 987.12 (5) Å3 and Z = 4. Final R = 4.9% [comparable with the R(F) of single-crystal work]. The structure exhibits the triangular prismatic Ta coordination about the P atoms and the dense packing of the Ta atoms, both familiar in many metal-rich phases formed between transition metals and non-metals of type P, As, S and Se.
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  • 47
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    Applied crystallography online 13 (1980), S. 611-611 
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    Notes: In the paper Revised and new crystal data for indium selenides by Popovic, Tonejc, Grzeta-Plenkovic, Celustka & Trojko [J. Appl. Cryst. (1979), 12, 416–420] it was concluded that P6122 or P6522 was the probable space group of the second high-temperature, γ, phase of In2Se3. Also, in the paper Phases, lattice parameters and thermal expansion of (GaxIn1−x)2Se3, 1 ≥ x ≥ 0, between room temperature and melting point by Tonejc, Popovic & Grzeta-Plenkovic [J. Appl. Cryst. (1980), 13, 24– 30] the same space groups were suggested for the phase γ1, existing in the In-rich region. However, the space group in both cases should be P61 or P65. This is in agreement with the work of Likforman, Carré & Hillel [Acta Cryst. (1978), B34, 1 5] who solved the crystal structure of one of the forms of In2Se3, and with the work of Schulte-Kellinghaus & Krämer [Acta Cryst. (1979), B35, 3016 3017] who solved the crystal structure of AlInS3. Likforman, Carré & Hillel [Acta Cryst. (1978), B34, 1 5] call their phase the low-temperature form of In2Se3.
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    Applied crystallography online 15 (1982), S. 251-254 
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    Notes: Changes in the microporosity of several types of Brazilian high-ash coals have been analyzed by small-angle X-ray scattering as a function of thermal treatment. Pore size, determined using Guinier plots, decreased following thermal treatment of the samples. The modification of porosity induced by thermal treatment was similar for high-ash and low-ash coals, from which it may be inferred that mineral content is not a determining factor in the process of pore formation. Internal surface area for the samples was calculated with SAXS data. A correlation is established between the internal surface area values obtained and the carbon content and heat-treatment temperatures of the samples.
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    Applied crystallography online 15 (1982), S. 279-281 
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    Notes: Crystal data for the series of piperazinium bis(n-alkanoates) of the type 2[CxH2x − 1O2−] [C4H12N22+] for x = 1 to 16 are presented. Most of these compounds have triclinic unit cells whose dimensions, obtained from single-crystal work, have been used to index their powder diagrams. The a ({\bar a} = 5.718 Å) and b ({\bar b} = 7.481 Å) cell dimensions remain nearly constant while the c dimension and the volume of the unit cell increase linearly with x, the number of carbon atoms in the alkanoate anion. Presumably the aliphatic sequence in the alkanoate anion adopts the fully extended conformation and lies in the bc plane and nearly along the c direction.
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    Applied crystallography online 14 (1981), S. 226-229 
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    Notes: A numerical procedure using orthogonal polynomials is used for extracting the background in measured spectra. An X-ray spectrum obtained with the energy-dispersive method is considered as an example.
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    Applied crystallography online 15 (1982), S. 461-462 
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    Notes: Lattice-constant thermal expansions, Δa/a and Δc/c, have been measured on α-HgI2 single crystals from 293 K up to the red-to-yellow transition temperature. The curves Δa/a(T) and Δc/c(T) are linear. The thermal expansion coefficients are determined: α[100] = (1.0 ± 0.1) × 10−5 K−1 and α[001] = (4.6 ± 0.1) × 10−5 K−1. No evidence of a red-to-orange phase transition could be found.
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  • 52
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    Applied crystallography online 15 (1982), S. 452-460 
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    Notes: Total neutron scattering data were collected on sputtered YFe2 at 298 K and TbFe2 at 423 K with a wavelength of 0.7 Å. The TbFe2 data were collected above the magnetic ordering temperature of 383 K. In addition, the elastic neutron scattering of TbFe2 was measured with the use of a pyrolytic graphite analyzer at a wavelength of 1.5 Å, and its total X-ray scattering was measured with Mo radiation and a silicon-lithium drifted detector. Experimental radial distribution functions, with statistical error limits, were calculated. Errors due to an incorrect background, scaling of the data and termination effects were minimized. The scale and shape of the experimental background and the coordination numbers, internuclear distances and disorder parameters, for the first six coordination spheres, have been determined. The contribution of paramagnetic inelastic scattering from TbFe2 to the total neutron scattering is quite appreciable. The shape of the background scattering, which goes through a maximum, is indicative of residual coherence and suggests short-range magnetic ordering where neighboring atom spins are aligned. These effects are not observed in YFe2, nor in the elastic TbFe2 data. The metallic glasses have a structural topology which is quite different from that found in their crystalline analogues. The transition-metal substructure, consisting of corner-sharing tetrahedra, is the only aspect of the crystalline topology preserved in the amorphous phase. The structural parameters suggest a tendency of the rare-earth atoms to cluster, thereby decreasing the number of Fe nearest neighbors relative to the crystalline structure.
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    Applied crystallography online 15 (1982), S. 55-59 
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    Notes: By using data from the Wallace & Ward [J. Appl. Cryst. (1975), 8, 255–260] cylindrical texture camera integrated with other traditional X-ray powder film techniques for very low and very high diffraction angles, a new high-temperature modification of CeO2 was identified and indexed resulting in a trigonal or hexagonal unit cell with a = 8.36(2) and c = 10.42(2) Å, (axial ratio 1.264) and Z = 16. The new phase is an oxidation product of CeO2-doped hot-pressed silicon nitride. It can be quenched to room temperature under appropriate conditions. Its stability on reheating is strictly related to its interaction with the silicate phase.
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    Applied crystallography online 15 (1982), S. 60-64 
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    Notes: Multiple electron scattering between weak beams has been used as the basis for a simple method to determine the absolute polarity of some non-centrosymmetric crystals. For crystals with the sphalerite structure many orientations have been found in which small departures from centrosymmetry produce large effects on the convergent-beam diffraction patterns (microdiffraction). The effects are reasonably independent of thickness and so can be analyzed qualitatively without the use of computers.
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    Applied crystallography online 15 (1982), S. 570-571 
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    Notes: A method is proposed for unambiguously indexing X-ray multiple diffraction patterns obtained with irregularly shaped crystals on a four-circle diffractometer. The method is derived from the orientation matrix together with the operation of crystal rotation. It is shown that this method facilitates the procedures in the experimental method for phase determination.
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    Applied crystallography online 15 (1982), S. 574-576 
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    Notes: Unit-cell constants for synthetic fluoroalleghanyite compounds have been determined by the refinement of X-ray powder diffraction data. Manganese norbergite: Pbnm, a = 4.862(2), b = 10.797(3), c = 9.188(2) Å, U = 482.4(4) Å3, Z = 4; alleghanyite: P21/b, a = 4.871(2), b = 10.818(6), c = 8.206(5) Å, α = 108.58(5)°, U = 414.1(7) Å3, Z = 2; manganhumite: Pbnm, a = 4.888 (2), b = 10.712(2), c = 21.749(6), U = 1138.8(5) Å3, Z = 4; sonolite: P21/b, a = 4.889(1), b = 10.668(3), c = 14.239(5), α = 100.83(5)°, U = 731.9(5) Å3, Z = 2. The JCPDS Powder Diffraction File numbers are: for manganese norbergerite 33–1500; for alleghanyite 33–1499; for manganhumite 33–1498; for sonolite 33–1497.
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    Applied crystallography online 15 (1982), S. 577-577 
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    Applied crystallography online 15 (1982), S. 577-578 
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    Applied crystallography online 15 (1982), S. 579-579 
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    Applied crystallography online 15 (1982), S. 579-580 
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    Applied crystallography online 15 (1982), S. 116-119 
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    Notes: Three members of a new family of phases, Li3Mg2XO6: X = Nb, Ta, Sb, have been prepared by solid-state reaction of MgO and Li3XO4. Unit-cell parameters of Li3Mg2TaO6 determined by electron diffraction and refined by X-ray powder diffraction are a = 8.883(2), b = 5.802(2), c = 17.437(6) Å, with space group Fddd; z = 8. Powder diffraction data of Li3Mg2NbO6 and Li3Mg2SbO6 were indexed by analogy with those of Li3Mg2TaO6 and unit-cell dimensions obtained by least-squares refinement: Li3Mg2NbO6 a = 8.552(2), b = 5.897(1), c = 17.721(5) Å; Li3Mg2SbO6 a = 8.614 (1), b = 5.908(1), c = 17.759(5) Å.
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    Applied crystallography online 15 (1982), S. 590-593 
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    Notes: The structure of the transition phase M′ in AlZnMg alloys has been studied by Buerger X-ray precession photographs and transmission electron microscopy. The M′ phase, also called η′ or R, has a hexagonal or pseudo-hexagonal cell with a = 4.96, c = 14.03 Å. It is confirmed that M′ precipitates are hexagonal platelets with the following epitaxy: (00.1)M′//(111)Al and |10.0|M′//1{\bar 1}0|Al. It is shown that none of the known models of the unit cell accounts for the observed scattered intensities.
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    Applied crystallography online 15 (1982), S. 602-604 
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    Notes: An improved `substitution method' for the separation of X-ray diffraction α1−α2 doublets is based on the possibility of refining both the proportionality constant between the α1 and α2 contributions to the line intensity and the doublet separation expressed in terms of the diffraction angle or of a related variable in the reciprocal space. Optimization of these two parameters, with a proper evaluation of the error, clearly shows the statistical nature of the oscillations appearing on the high-angle side of the pure α1 component after correction; their elimination by polynomial smoothing can therefore be performed and a procedure is suggested for achieving this result. A computer program, based on these principles, has been written and tested in many practical cases.
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    Applied crystallography online 15 (1982), S. 611-614 
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    Notes: The precipitation behavior in the Ti–27at.%Nb–6at.%Ta–6at.%Zr alloy aged at 643 K was examined by means of time-of-flight neutron small-angle scattering. When the alloy was aged, fine-scale α precipitates appeared. During the precipitation process, each precipitate grew in size, but the total number of precipitates remained nearly constant up to 1 Ms of ageing. The increase of critical superconducting current density could be connected with increasing size of α precipitates. The specimen for the measurements consisted of a composite containing 3721 filaments in a copper matrix. The use of neutrons was shown to give great advantages for the investigation of precipitation phenomena.
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    Applied crystallography online 15 (1982), S. 632-632 
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    Notes: The wrong original was used for Fig. 6(b) of Gastaldi, Jourdan, Marzo, Allasia & Jullien [J. Appl. Cryst. (1982), 15, 391–395]. The correct version of Fig. 6(b) is given. In Fig. 6(c) the growth time increases from right to left.
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    Applied crystallography online 15 (1982), S. 635-636 
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    Notes: The high-temperature paraelectric phase of dicalcium lead propionate, DCLP, at 363 ± 5 K is tetragonal, with a = 12.574 (6), c = 17.403 (9) Å, V = 2751.4 Å3, Z = 4 and corresponds to the space group P41212 (or P43212). The thermal expansion curve shows the transition somewhere between 328 and 343 K.
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    Applied crystallography online 15 (1982), S. 638-638 
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    Applied crystallography online 15 (1982), S. 638-639 
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    Applied crystallography online 15 (1982), S. 639-639 
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    Applied crystallography online 15 (1982), S. 640-676 
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    Applied crystallography online 15 (1982), S. 182-189 
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    Notes: The method of determining the thickness of a diffuse phase boundary with density profile governed by equilibrium conditions is proposed. It follows the well known procedure of analyzing the deviations from Porod's law. Errors in the obtained boundary thickness, owing to the statistical scatter in the intensity data and to the difficulty of separating the effect of density fluctuations within the phases, are examined. For this purpose, scattering curves are synthesized on the basis of a well defined model structure with known boundary thicknesses. These synthesized curves, when analyzed according to the proposed method, yield the correct boundary thickness under favorable conditions, but are also shown to lead to very erroneous results in some cases.
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    Applied crystallography online 15 (1982), S. 211-215 
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    Notes: Monoclinic Gd2SiO5 has been investigated by high-resolution electron microscopy (HREM) at 100 kV. Structure images are observed in the [100] and [001] projections and calculations of the image contrast using the multislice approximation are carried out to interpret the observations. For thin samples the image fit is improved by Fourier filtering of the observed images. For thicker samples the fit is found to be very sensitive to small tilt deviations of the zone axis to the electron beam. For defects observed in a fast-cooled specimen, a model in which Gd atoms replace Si atoms in segments along the (100) plane is proposed and tested by contrast calculations. These defects may be one of the reasons for deviations from stoichiometry as frequently observed in rare-earth silicates.
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    Applied crystallography online 15 (1982), S. 241-244 
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    Notes: A low-temperature camera for single-crystal X-ray investigation between 28 and 350 K has been developed for a modified Weissenberg goniometer. Cooling is provided by a double-stage cryorefrigerator which is firmly attached to the low-temperature camera. Stranded copper cables ensure a flexible heat transfer between crystal and cold finger allowing a crystal rotation of 180°. Compared to the usual Weissenberg technique almost no further limitation is given on the accessible angular range of the scattered radiation.
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    Applied crystallography online 15 (1982), S. 248-248 
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    Notes: The X-ray powder data have been obtained for a new phase MoGa5(CuS2)0.0556. The powder patterns were indexed on the basis of a tetragonal body-centred unit cell with the lattice constants a = 12.872, c = 5.284 Å, c/a = 0.410, dm = 6.825(8), dx = 6.869 Mg m−3, Z = 8.
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    Applied crystallography online 15 (1982), S. 249-249 
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    Applied crystallography online 15 (1982), S. 250-250 
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    Applied crystallography online 15 (1982), S. 255-259 
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    Notes: The identification of twofold axes is straightforward if the cell is based on three of the shortest lattice translations. The distribution of twofold axes in space fixes the lattice symmetry and most conventional cell edges. A program based on this approach has been written. It works for the seven cases with minimum branching of the algorithm.
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    Applied crystallography online 15 (1982), S. 266-274 
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    Notes: The commonest natural diamonds (classification type Ia) contain platelet defects on {100}, usually with mean diameters in the 20 to 100 nm range, which generate disorder diffuse X-ray reflections in the form of (100) spikes through reciprocal-lattice points. Corresponding spikes in electron diffraction patterns of diamonds, recorded with 100 and 120 kV electrons, have been investigated. It has been established that (100) spikes appear most strongly in electron diffraction patterns of diamonds very rich in platelets, and are absent in the case of platelet-free diamonds (types IIa and IIb). Spikes from diamonds containing relatively large platelets are sharper than those from diamonds containing very small platelets. Multiple scattering of electrons prevents measurement of the dependence of spike intensity upon diffraction order as can be done in the X-ray case. Some experiments with spike electron reflections have been performed that are impossible in the X-ray case. It has been shown that when the crystal volume sampled by the electron beam contains only one platelet, then the spike distribution reduces to a pattern containing only spikes normal to the platelet concerned. Also, dark-field weak-beam microscopy has been applied, by selecting one spike only in the diffraction pattern, to identify orientations of small platelets through the imaging of only those platelets normal to the spike selected.
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    Applied crystallography online 15 (1982), S. 301-307 
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    Notes: The amplitude and phase of a wave scattered by an adsorbed layer can be deduced from the modifications of the Bragg peak of the powder by adsorption. The treatment of experimental data involves the interpretation of a function of the extra intensity detected and has the advantages of an integrated intensity method. Powders containing crystallites limited by several types of faces can be studied. The Co3O4 sample studied is limited only by (110) and (111) faces of respective areas 11 and 27 m2 g−1. The (111) planes terminating crystallites contain oxygen covering a layer of cobalt in octahedral sites. Other possible terminating layers are ruled out for (111) planes. The structures of the bidimensional layers of argon on (110) and (111) planes are determined.
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    Applied crystallography online 15 (1982), S. 315-322 
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    Notes: A correction for the unavoidable truncation of line profiles and an improved correction for the inherent curvature of the variance–range function are discussed. An analytical procedure for making the corrections is proposed and applied to theoretical and practical small-crystallite line profiles. An alternative procedure for obtaining the integrated intensity, and hence the integral breadth, and the variance (Fourier) apparent size is also presented.
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    Applied crystallography online 15 (1982), S. 289-300 
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    Notes: As a consequence of several technological developments, the speed and sensitivity of solution X-ray (and neutron) scattering studies have recently risen by factors which may be as large as 105; formal problems – like assessing the information content of the data and retrieving that information in structural terms – have thus become of immediate practical interest. The general problem of the information content of scattering experiments is discussed; its mathematical expression is derived, which depends on both the experimental data (observed values and estimated accuracy) and the a priori stochastic assumptions on the structure of the sample. The practical application of these notions to solution scattering studies involves several steps, three of which – choice of the degrees of freedom, data reduction and error analysis – are dealt with in this work. The first step is to specify the minimal number of independent parameters necessary and sufficient to describe the whole of the scattering properties of the system. Whenever the solute particles are of finite dimensions the entire scattering curve is defined by its values at a one-dimensional lattice; if, moreover, the asymptotic trend of the scattering curves is known, then the degrees of freedom are the ideal intensities at a finite number of points plus a small number of parameters describing the asymptotic trend. It is also possible to include among the degrees of freedom a few subsidiary parameters like the normalization factors. The next step is, starting from a composite set of data, to determine the most probable numerical value of each degree of freedom and to evaluate its range of uncertainty. This is discussed within the framework of variable-contrast studies, assuming that the invariant-volume hypothesis is fulfilled. An algorithm is formulated which treats all the experimental observations and determines simultaneously all the degrees of freedom and the error matrix. The algorithm also allows one to introduce additional linear constraints on the degrees of freedom. As an example, the algorithm is applied to solution X-ray scattering data recorded with a low-density serum lipoprotein. The determination of the maximal chord of the particle – an important parameter in the informational analysis – turns out to be rather tricky.
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    Applied crystallography online 15 (1982), S. 330-337 
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    Notes: The design and operation of a focusing camera for high-resolution macromolecular crystallography with synchrotron radiation (SR) are described. The performance of this service-oriented instrument is evaluated on the basis of five years of use. Standard procedures for data collection, data processing and data reduction have been modified to take unusual features of the SR source into account; the effect of polarization is thoroughly discussed.
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    Applied crystallography online 15 (1982), S. 338-351 
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    Notes: Expressions are developed for reflecting range from various models, and the practical application of these in terms of reflection prediction and calculation of partiality is discussed here for conventional sources. Synchrotron sources utilizing focusing monochromator systems, where the wavelength of the radiation incident at the sample is correlated with the angular direction of that radiation, are dealt with elsewhere. Even for conventional sources spectral dispersion is shown to be an important factor, particularly in the case of high-resolution data. The various published methods are discussed and expressions are derived from first principles showing that all are inherently equivalent, differing only when approximations are used, and revealing a missing factor of two in the treatments of Rossmann [J. Appl. Cryst. (1979), 12, 225–238] and Rossmann, Leslie, Abdel-Meguid & Tsukihara [J. Appl. Cryst. (1979), 12, 570–581]. Particular emphasis is placed on the method which uses a spherical reciprocal-lattice volume element whose dimensions are designed to reproduce the expected or observed reflecting ranges, showing that for all practical purposes the effects of beam cross-fire, mosaic spread and spectral dispersion can be adequately simulated by such a volume. The equations for reflecting range are of particular interest in the electronic stationary-picture method and in the use of electronic area detectors.
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    Applied crystallography online 15 (1982), S. 361-374 
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    Notes: In the Rietveld method of analysing powder diffraction data, the crystal structure is refined by fitting the entire profile of the diffraction pattern to a calculated profile. There is no intermediate step of extracting structure factors. The method was applied first to diffraction patterns recorded with neutrons at a fixed wavelength. It has now been used successfully for the treatment of results from the four categories of experimental technique, with neutrons or X-rays as the primary radiation and with the scattered intensity measured at a fixed wavelength or at a fixed scattering angle. In this article we discuss the application of the Rietveld method to each of these techniques.
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    Applied crystallography online 16 (1983), S. 251-256 
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    Notes: Integrated X-ray Bragg intensities from Nb single crystals have been measured as a function of H concentration and scattering vector along high-symmetry directions. The observed attenuation can be described in terms of a static Debye–Waller factor (DWF) due to the static displacements of the Nb lattice atoms around the dissolved H. The crystals were loaded with H in situ on the X-ray diffractometer. The static DWF was determined from the ratio of the intensities from a crystal with and without H. Corrections are necessary for several magnitudes which change with the lattice-parameter change and the change of the thermal displacements upon the uptake of H. The measured static DWF is proportional to the H concentration c(H/Nb) for c≤0.30 and the square of the scattering vector K2 for small K, as expected from theory. From analysis of the static DWF the static displacements of the Nb atoms closest to the H impurity u1 = 0.1 Å were determined.
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    Applied crystallography online 16 (1983), S. 276-276 
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    Notes: Crystal data for the Schiff bases 2-(4-methyl-2-pyridinyliminomethyl)phenol (salampy) and 2-(4,6-dimethyl-2-pyridyliminomethyl)phenol (saladimpy) are reported. Salampy: C13H12N2O, Mr = 212.0, P21/c, a = 11.772(4), b = 7.5386(7), c = 15.154(5) Å, β = 124.89 (2)°, V = 1103.1(4) Å3, Dm = 1.24, Dx = 1.28 g cm−3, Z = 4; saladimpy: C14H14N2O, Mr = 226.0, P212121, a = 21.585(5), b = 8.8285(8), c = 6.2952(6) Å, V = 1199.6(3) Å3 Dm = 1.22, Dx = 1.25 g cm−3, Z = 4. The JCPDS Diffraction File No. for C13H12N2O is 33-1999, for C14H14N2O 33-1998.
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    Applied crystallography online 16 (1983), S. 277-277 
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    Notes: The air-sensitive title hydride [Hf(C9H13)2H2]2 was prepared by hydrogenolysis of (t-BuCp)2HfMe2 [Couturier, Tainturier & Gautheron (1980). J. Organomet. Chem. 195, 291–306] and crystallized from a solution in heptane or toluene and hexane. The compound is triclinic with the following cell parameters: a = 7.22(3), b = 10.31(4), c = 12.47(6) Å, α = 80.4(4), β = 74.6(4)°, γ = 72.1(3)°, V = 847 Å3, Z = 1, Dx = 1.67 Mg m− 3. Powder diffraction data were obtained from Debye–Scherrer photographs. The extended version of the paper examines several examples where Zr or Hf hydrides are monomers or dimers and shows that this structure is very similar to the related [(MeCp)2ZrH2]2 compound [Jones & Petersen (1981). Inorg. Chem. 20, 2889–2894]. This similarity and spectroscopic data show that the molecule probably has a center of symmetry situated between the two Hf atoms and the two bridging H atoms. The JCPDS Diffraction File No. for [Hf(C9H13)2H2]2 is 33-1996.
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    Applied crystallography online 16 (1983), S. 284-284 
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    Applied crystallography online 16 (1983), S. 295-303 
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    Notes: The integrated X-ray reflectivity of elastically bent, but otherwise perfect, crystals are calculated for Laue-type reflections covering the entire curvature range. Anomalous transmission and elastic anisotropy are taken into account, and it is shown that both these effects affect appreciably the reflected intensities for both weakly and strongly bent crystals. The validity of the reflectivity-versus-curvature relation thus obtained is experimentally confirmed for a number of reflections from silicon crystals. The implications of the experimental results to brittle fracture are discussed.
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    Applied crystallography online 16 (1983), S. 317-324 
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    Notes: A sequence of steps is given for making use of the information available on convergent-beam electron diffraction patterns from high-symmetry zone axes for crystal point- and space-group determination.
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    Applied crystallography online 16 (1983), S. 354-356 
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    Notes: By use of a high-temperature camera designed for in situ synchrotron-radiation X-ray topography the α−β transition was investigated in a Z-cut synthetic-quartz sample. Preliminary dynamical observations on movement of the boundaries between α and β phases and α1 and α2 domains are reported.
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    Applied crystallography online 16 (1983), S. 357-357 
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    Notes: The crystal structure of α-HgO2 was determined using X-ray powder diffraction. The crystal is C-centered monoclinic, C2/m, a = 4.470(2), b = 5.459(2), c = 3.519(2) Å, β = 108.45°, Z = 2, Dx = 9.48 g cm− 3. The variable coordinates of oxygen atoms from the peroxide dumbbell were determined as x = 0.476, z = 0.280. The final R is 0.047. The JCPDS Diffraction File No. for α-HgO2 is 33-1489.
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    Applied crystallography online 16 (1983), S. 358-358 
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    Notes: PROMETHEUS is a Fortran IV program system for investigation of anharmonic thermal vibrations in crystals, using elastic X-ray or neutron data. Three different anharmonic temperature-factor equations can be used, one of them up to sixth-order terms. The corresponding probability densities and mean effective atomic potentials can be calculated. Programs for correction of isotropic thermal diffuse scattering and of isotropic and anisotropic extinction are included. Fast averaging of symmetrically equivalent reflections combined with extended reflection statistics is possible. Calculations of Fourier syntheses and their errors and of Patterson functions can be carried out and the corresponding contour maps can be plotted.
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    Applied crystallography online 15 (1982), S. 540-541 
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    Notes: Second-harmonic generator tests for non-centrosymmetry have been applied to five monoclinic potassium feldspars. Four samples yielded null results; one specimen displayed a positive test for non-centrosymmetry.
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    Applied crystallography online 15 (1982), S. 564-566 
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    Notes: Clays prepared by sedimentation from aqueous suspension were shown to contain aggregates much larger than individual clay particles. Small-angle X-ray scattering data were obtained with an automated Bonse–Hart instrument. The distance distribution functions for the clay aggregates were obtained using the Glatter indirect Fourier transform method. The distance distribution function extended to over 200000 Å, and the average radius of gyration was over 50000 Å in the most extreme cases.
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    Applied crystallography online 15 (1982), S. 567-569 
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    Notes: The intensity of the small-angle X-ray and neutron scattering from a polydisperse system of randomly oriented independently scattering particles is shown to be proportional to h−α for all values of the scattering vector h when the distribution of particle dimensions is proportional to r−(2d + 1 − α), where h = 4πλ−1 sin(θ/2);θ is the scattering angle; λ is the wavelength; r is the maximum dimension of a particle; and d is the number of dimensions of the particles. The value of α lies in the interval 0 〈 α 〈 ω, where ω = 4, 2, and 1 for d = 3, 2, and 1 respectively. This relationship between the scattered intensity and the particle-dimension distribution does not depend on the shape of the particles in the polydisperse system, provided that the particle-shape distribution is independent of the distribution of particle dimensions.
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    Applied crystallography online 15 (1982), S. 571-573 
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    Notes: A simple method is described for increasing the lifetimes for several crystals of proteins and viruses during collection of high-resolution X-ray diffraction data on film. Crystals are mounted in a capillary filled with mother liquor, with cotton lint fibers nested against them to prevent movement. Some results and limitations of the method are discussed.
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    Applied crystallography online 16 (1983), S. 508-511 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The finite height of the detector slit of a powder diffractometer has three observable effects: (1) the peak is shifted by an amount that is proportional to −cot 2θ; (2) the peak is broadened by an amount proportional to cot22θ; (3) an asymmetry is introduced into the peak shape that depends on cot32θ. If the underlying instrumental resolution function has a Gaussian shape, the slit height effects can be approximated, over a rather broad range of shapes for the vertical resolution function, by an Edgeworth series making use of one adjustable parameter. This peak shape function is compared with experimental observations and with other shape functions that have been proposed. A well characterized peak shape is at least as important as resolution when the data are to be used for structure refinement by the Rietveld technique, and diffractometers should be designed so as to keep the slit height within the range that leads to shapes that can be described mathematically. Diffractometers with multiple detectors can usefully have different vertical divergences for detectors that cover different angular ranges.
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  • 99
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 578-578 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 100
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 579-579 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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