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  • Articles  (38,078)
  • American Association for the Advancement of Science (AAAS)  (14,840)
  • International Union of Crystallography (IUCr)  (12,689)
  • Cell Press
  • 1980-1984  (23,631)
  • 1975-1979  (14,447)
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  • 101
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    Density-contrast studies of macromolecules in solution. Cross verification of X-ray scattering and pycnometry experiments (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 466-472 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The density-contrast method, commonly used in X-ray (and neutron) small-angle scattering studies of macromolecules in solution, can yield a wealth of information if; (a) the solute is monodisperse and the solution is ideal: (b) each macromolecule in solution has a volume associated with it inside of which the density distribution is independent of the density of the solvent. More specifically it has been pointed out that in this case an expression of the molecular weight can be obtained which does not involve the partial specific volume, provided that the X-ray experiments are performed on an absolute scale. On the other hand, it is well known that X-ray scattering experiments on an ideal solution of identical macromolecules can yield the molecular weight for any composition of the solvent, provided solute, solvent and partial specific volumes are defined and measured at constant chemical potential. Therefore a combination of X-ray scattering and densimetry experiments allows one to verify to what extent condition (b) holds true. Such a set of experiments has been performed on Rhesus monkey low-density serum lipoproteins, the solvent being water containing variable amounts of NaBr. It is concluded that in this case condition (b) is fulfilled. Moreover several important aspects of the analysis of the X-ray scattering curves can be verified.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889878013606
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  • 102
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    The measurement of the locations and radii of gyration of proteins in the 30S ribosomal subunit of E. coli by neutron scattering (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 479-482 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The theory of the technique currently in use for measuring distances between subunits in macromolecular aggregates by neutron small-angle scattering is outlined. It is shown that estimates for the radii of gyration of subunits within aggregates can be extracted from neutron distance data, in addition to the distances themselves. The current status of efforts to apply these methods to determine the structure of the E. coli ribosome is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889878013643
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  • 103
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    Al2SiO5, Al2GeO5 and Cr2GeO5 kyanites: X-ray powder data and infrared absorption spectra (1975)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 329-332 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Kyanite phases Al2SiO5 (I), Al2GeO5 (II) and Cr2GeO5 (III) were synthesized at 20 kb/1000°C (I, II) and at 1 atm/1150°C (III). Powder X-ray patterns for II and III are presented in comparison with that of I. Triclinic lattice constants are a0 = 7.127 (7.253, 7.422), b0 = 7.858 (8.011, 8.244), c0 = 5.570 (5.649, 5.815) Å, α = 89.99 (89.97, 90.58), β = 101.22 (101.23, 101.10), γ = 106.04 (106.05, 106.01)°, and V0 = 293.6 (308.9, 339.9) Å3 for the kyanite phases I (II, III, respectively). Infrared absorption spectra of I (II, III) were measured between 1400 and 200 cm−1. Band shifts produced by the isomorphous substitutions allow tentative band assignments of the Al2SiO5-kyanite spectrum: 1032, 1009, 940 cm−1 ν3 (SiO4); 898 cm−1 ν1 (SiO4); 720, 438 cm−1 ν4, ν2 (SiO4) ?; banes between 674 and 505 cm−1 and at 467 cm−1 are mainly due to octahedral Al–O vibrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889875010540
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  • 104
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    Neutron-scattering studies of chromatin subunits under a variety of contrast conditions (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 483-484 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Neutron-scattering studies of chromatin core particles in solutions containing various mixtures of D2O/H2O and small molecules (glycerol) show that the water closely associated (or bound) with the particles is largely in the outer DNA-rich regions. This confirms the fact that the particles contain a core composed of the hydrophobic regions of histone proteins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889878013655
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  • 105
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    Die Mineralfunde der Schweiz by R. L. Parker (1975)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 343-344 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889875010655
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  • 106
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    Notes and News (1975)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 343-343 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889875010643
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  • 107
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    Méthode du faisceau convergent: application à la sélection et à l'étude de cristaux polytypiques (1975)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 352-355 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An attractive use of a convergent-beam camera is described. Its advantages, with respect to classical methods, are pointed out. The short exposure time provided by this device is very useful in the selection and detailed study of polytypic crystals. Some X-ray photographs obtained from a titanium sulphide polytypic crystal are displayed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889875010679
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  • 108
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    Méthode d'analyse du profil de bande produite par des feuillets diffractants ayant une forme anisométrique (1975)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 365-371 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Solids characterized by lamellar structure are often made from ribbon or lath-shaped sheets. Such a morphology has been observed in phyllosilicates (hectorite or nontronite, for example) and in carbon fibres. This contribution aims to show that elongated planar sheets can be detected from the profile of the X-ray diffraction bands yielded by the powdered solid. The numerical technique originally developed by Brindley & Méring [Acta Cryst. (1951). 4, 441–447] for isometric layers, has been extended to ribbon or lath-shaped elementary layers. An example of application is given when the sheet is a carbon layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889875010709
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  • 109
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    Etude par diffraction des rayons X sur poudre de la transition ordre–désordre du ferrocène Fe(C5H5)2 (1975)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 380-385 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: About fifty X-ray powder diagrams were recorded in the range 15 to 295 K, by means of a prototype diffractometer and a high-efficiency cryostat, so that a very precise study of the anisotropic structural evolution of ferrocene could be made. The cell parameters and volume have been computed. These parameters present a discontinuity at 164 K; the cell is triclinic below and monoclinic above this temperature. The transition is first order. The principal thermal expansion coefficients have been computed and their evolution, in terms of temperature, has been related to the anisotropic change of the intermolecular contacts in the crystal. Assumptions about the mechanism of transition and about the ferrocene configuration in the ordered phase are expressed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889875010734
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  • 110
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    Precession photography: orienting crystals by means of the stereographic projection (1975)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 388-389 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A graphical construction on the Wulff net permits corrections on both arcs and the dial to be determined even if neither of the arcs is parallel to the film and/or the outer arc reading is large. The procedure requires that the orientation errors be multiplied by an arbitrary common factor smaller than ten, while the biggest multiplied error should be less than ten degrees: the corrections are obtained graphically and divided by the factor. Corrections thus obtained are within 10% of their true values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889875010758
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  • 111
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    Synthesè et données cristallographiques de trois polymolybdates de thallium I (1975)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 398-400 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Tl2Mo7O22 is monoclinic with space groupe C2/c or Cc and with a = 20,512 (6); b = 5,526 (2); c = 19,460 (6) Å; β = 125,20 (3)°: Z = 4. Tl2Mo4O13 is orthorhombic with space group Pbca and with a = 7,583 (3); b = 15,409 (3); c = 18,798 (3) Å; Z = 8. Tl7Mo2O7 is monoclinic with a = 8,427 (2); b = 5,690 (2); c = 7,935 (2) Å; β = 108,90 (2)°; Z = 2. The indexed powder diagrams are given.
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    URL: http://dx.doi.org/10.1107/S0021889875010813
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  • 112
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    Acta Crystallographica and Journals of Applied Crystallography (1975)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 402-402 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889875010849
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  • 113
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    Silicon carbide – 1973. (Proceddings of the Third International Conference, Florida, 1973) edited by R. C. Marshall, J. W. Faust Jr and C. E. Ryan (1975)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 403-403 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889875010874
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  • 114
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    Crystal data and structural relation between Pb6GeO8.Pb11Ge3O17 and PbO (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 307-310 
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    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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    URL: http://dx.doi.org/10.1107/S0021889880012125
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  • 115
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    Crystal data for AgGaxIn1−xSe2 and CuGaxIn1−xSe2 (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 311-315 
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    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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    URL: http://dx.doi.org/10.1107/S0021889880012149
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  • 116
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    Commission on Crystallographic Apparatus. Microdensitometer Project report I. Inter-Experimental Agreement (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 318-337 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889880012174
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  • 117
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    Longer filament lifetimes for rotating-anode X-ray machines using a beam-deflecting magnet (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 338-339 
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    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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    URL: http://dx.doi.org/10.1107/S0021889880012198
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  • 118
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    Small-angle X-ray scattering studies on polymer chain conformations in concentrated solutions and in bulk (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 514-519 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The use of the polymers tagged with heavy atoms in random positions along the chains (randomly tagged polymers) in small-angle X-ray scattering is proposed as a new method for measuring the chain conformations in concentrated solutions and in bulk polymers. The experimentally determined excess scattering from the tagged chains dispersed in the system is shown to be proportional to the scattering function of the hypothetical chains that have no tags but have the conformation of the tagged chains when the heavy atoms have sufficiently large scattering power. It has been experimentally verified that the effect of the tags on the chain conformation can be eliminated by the extrapolation of the apparent values, measured for a series of tagged polymers with various tag content, to zero tag content. The radii of gyration of the polystyrene chains (M = 1.1 × 105) in the bulk and in concentrated solutions in a good solvent and a θ-solvent have been determined. The chain dimension in a good solvent (toluene at 25°C) decreases rapidly first and then gradually approaches the unperturbed dimension with increasing polymer concentration. The dimension in a θ-solvent (trans-decalin at 21.2°C) is independent of the polymer concentration. The conformation of the polystyrene chains in the bulk was found to be a Gaussian coil.
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    URL: http://dx.doi.org/10.1107/S0021889878013771
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  • 119
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    Small-angle X-ray scattering of polyethylene single-crystal suspensions (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 525-530 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Small-angle X-ray scattering from oriented mats and random suspensions of polyethylene single crystals has been studied. A modification of the Guinier equation for platelets was derived to accommodate the two-phase nature of polymer lamellae. This modification also permitted the modelling of various degrees of interaction between lamellae and suspending media. Dried crystal mats show an increase in fold period on contact with potential solvents. Crystals which have never been dried show no evidence of penetration of the fold surface by the same liquids. Apparently the drying process causes a reorganization of the surface of the lamellae. Since the fold surfaces of crystals in suspension are unaffected by the liquids used, it is reasonable to assume a `tight' fold surface model. Crystallinities calculated with this model are in excellent agreement with recent differential scanning calorimetric data on crystals kept in suspension.
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    URL: http://dx.doi.org/10.1107/S0021889878013795
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  • 120
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    Organization in semi-dilute polyelectrolyte solutions observed by small-angle neutron scattering (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 519-523 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The study of semi-dilute polyelectrolyte solutions by small-angle neutron scattering shows that the correlation function S(q) of all the chains presents a peak for a value q = qh of the scattering vector q. This is taken as evidence for some organization among the elongated polyions. This phenomenon has been observed for a fraction of polymethacrylic acid of very low molecular weight. The experiments show essentially: (1) the progressive vanishing of the peak with the addition of a neutral salt at constant polyelectrolyte concentration; (2) the variation of qh with the polyelectrolyte concentration c, qh ∝ c1/2; (3) the decrease of the peak intensity as the charge density of the chain increases. These results, which indicate the important role of the electrostatic interactions on this organization phenomenon, are discussed in terms of a lattice model and a recently proposed isotropic model.
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  • 121
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    Determination of the interface distribution function of lamellar two-phase systems (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 535-539 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The concept of interface distribution functions [Ruland (1977). Colloid Polym. Sci. 255, 417–427] has been applied to the evaluation of the small-angle scattering of a series of polyethylene samples. The results indicate that the statistics of the lamellar stacking is not necessarily determined by next-neighbor interactions and that non-negligible volume fractions of amorphous domains outside the lamellar systems are observed in a number of samples.
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    URL: http://dx.doi.org/10.1107/S0021889878013813
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  • 122
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    An impurity-doped crystal plate as an X-ray monochromator (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 391-394 
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    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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    URL: http://dx.doi.org/10.1107/S0021889880012368
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  • 123
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    Notes and News (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 401-401 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    URL: http://dx.doi.org/10.1107/S0021889880012423
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  • 124
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    Appareil de microdéformation à chaud pour topographie aux rayons X. Application à des bicristaux de germanium (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 88-92 
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    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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  • 125
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    Assessment of synchrotron electron-beam damage in diamond by optical, cathodoluminescence and X-ray topographic methods (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 78-87 
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    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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    Crystal data for two kinds of molecular alloys between sebacic and dodecanedioic acids (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 93-95 
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    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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    Crystal data for hexamethylenetetraselenafulvalene-perfluorotetracyanoquinodimethane (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 95-96 
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    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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    A dynamic study of the crystallization of polyethylene from the melt (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 551-557 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Crystallization of a linear polyethylene from the melt was followed in situ with the ORNL 10-meter SAXS camera [Hendricks (1978). J. Appl. Cryst. 11, 15–30]. Specimens were rapidly cooled in the X-ray beam in tandem birdcage furnaces from 1̃80°C to temperatures between 115 and 126°C, and scattering patterns were recorded for 30 s in 50 s intervals. Because of this relatively high-speed data acquisition rate, it was possible to obtain data in time periods which were short compared to the rate of change of the scattering patterns. The SAXS curves showed shapes which changed continuously during crystallization. The scattering curves are the superposition of a zero-angle peak and a Bragg maximum. Guinier plots of the zero-angle peak manifest scattering by lamellae of constant thickness. The thickness value is nearly that expected for crystallites at these crystallization temperatures. A model in which skeletal spherulites form and then later fill in is consistent with these results. Decreasing SAXS intensity and changing Bragg peak intensities indicate crystal thickening during cooling to room temperature.
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    Small-angle X-ray scattering from block copolymers as an ideal model system for a pseudo two-phase solid texture (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 558-563 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The microdomain structure of polystyrene-polyisoprene A-B type block copolymers was analysed by small-angle X-ray scattering (SAXS) as an ideal model system for a pseudo two-phase solid structure. The structure was analysed in terms of spatial distribution, size, and the interracial structure of the dispersed domains of one component (A segments) in the matrix of the other (B segments). The SAXS analyses were performed with two collimating systems, a Rigaku Denki camera (essentially a four-slit system with the addition of Soller slits) and a Kratky camera, which had widely different slit-length and slit-width weighting functions and was used to investigate instrumental effects, especially the role of the Soller slits in the obtaining of reliable desmeared intensity data in the tail of the SAXS curve. Comparison of the results indicated that the Soller slits facilitate the accurate evaluation of the interfacial thickness from the desmeared intensity data in the tail. The accuracy of the infinite slit-height approximation and the effect of truncating the higher-order terms in Ih (the intensity associated with the interphase) on the estimated interfacial thickness are discussed. The infinite slit-height approximation leads to values 25–35% smaller than the exact value (23 Å), and the truncation also leads to a value of the interfacial thickness smaller (19 Å) than the value (23 Å) based on the full analysis. The value obtained is in good agreement with the values predicted from the statistical-mechanical theories of block copolymers in bulk.
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    Neutron small-angle scattering study of phase decomposition in Au–Pt (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 572-577 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Isothermal decomposition of a Au-60 at.% Pt alloy, quenched from the solid as well as the liquid state, has been studied with the D11 neutron small-angle scattering spectrometer at ILL, Grenoble. An incident neutron wavelength of 6.7 Å was used and measurements were carried out in the range of scattering vector [β = 4πsin θ/λ] from 2.8 × 10−2 to 21 × 10−2 Å−1. The preliminary results indicate that decomposition of this alloy at 550°C takes place by a spinodal mode, although deviations were observed from linear spinodal theory, even at very early times. Slower aging kinetics were observed in liquid-quenched alloy as compared with solid-quenched. Liquid quenching is more efficient in suppressing quench clustering than is solid quenching. However, liquid quenching yields an extremely fine-grained material, which thereby enhances discontinuous precipitation at grain boundaries, competing with decomposition in the bulk. A Rundman–Hilliard analysis was used for the early stages of the spinodal reaction to obtain an interdiffusion coefficient of the order of 10−16 cm2 s−1 at 550°C for the solid-quenched alloy.
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    Small-angle electron scattering in the transmission electron microscope (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 564-568 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Two methods for performing small-angle electron scattering (SAES) experiments in transmission electron microscopes are described: the long-camera-length method and the selected-area-diffraction method. It is shown experimentally that angular resolutions of a few microradians and a few tenths of milliradians, respectively, are easily obtained by these two methods. A number of examples of the application of SAES to problems in materials science are presented. The use of new high-brightness electron sources is expected to produce significant increases in angular resolution, and the use of electron-energy analyzers will permit the separation of most of the inelastic contribution to the SAES intensity distribution.
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    A small-angle neutron scattering study of the temperature and stress dependence of the microstructure of nimonic alloys (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 583-588 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The creep properties in high-temperature alloys are dependent on the presence of second and higher phase components. In particular in the nimonic group of alloys the size distribution and concentration of the γ′ phase are crucial factors in the resistance to creep. A possible mechanism for degradation of creep resistance is the Ostwald ripening of the γ′ phase. A sample of Nimonic 105 (Trademark of Henry Wiggin and Co. Ltd) was subjected simultaneously to a stress of 500 MPa and a temperature of 800°C in situ in the beam using a specially developed cell on the small-angle scattering facility (D 11A) at the Institut Laue Langevin. Scattering patterns were taken continuously and spectra were recorded every ̃20 min; the macroscopic creep was also recorded. Measurements were taken up to the point of fracture. A peak in the intensity was observed at a scattering vector κ (= 4π sin θ/λ) of 0.005 Å−1 which is believed to be the lowest value at which such an effect has been observed in alloys. The observed variation in the scattering after treatment for multiple scattering and absorption corrections is discussed in terms of particle size and size distribution.
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    A goniometer for the measurement of stresses in single crystals and coarse-grained specimens (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 128-131 
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    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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    The correlation function, intersect distribution and scattering from a cube (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 132-134 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    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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    Experimental separation of the coherent component of X-ray scattering prior to RDF analysis of non-crystalline polymers (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 135-140 
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    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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    Calcul du Profil des bandes de diffraction produites par des empilements de feuillets de nature différente (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 148-153 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    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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    Circular diffuse scattering from a niobium tungsten bronze, 3Nb2O5.8WO3, studied by 1 MV higher-resolution electron microscopy (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 141-147 
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    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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    An assessment of the performance of a diffracted-beam monochromator in single-crystal diffractometry (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 163-167 
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    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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    Small-angle X-ray scattering from solutions of flow-oriented colloidal particles (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 154-162 
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    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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    Small-angle scattering. Information content and error analysis (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 168-175 
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    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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    Design criteria for a laboratory EXAFS facility (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 3-7 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    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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    Neutron photographic measurements of protein single-crystal reflections (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 24-27 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    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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    A device for accurate single-crystal X-ray diffraction investigations at non-ambient temperatures: 83–1120 K (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 43-50 
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    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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    A fitting method for X-ray diffraction profiles (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 60-61 
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    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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    Crystal data for two series of solid solutions: (RbxK1−x)MgCr2(VO4)3 and (TlxK1−x)MgCr2(VO4)3 (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 61-62 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    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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    Crystal data for ferric molybdate: Fe2(MoO4)3 (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 64-65 
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    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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    Crystal data for high-temperature As2O5 (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 68-68 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    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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    Characteristics of a flat multiwire area detector for protein crystallography (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 85-93 
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    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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    An assessment of instrumental parameters which control the accuracy of stress measurement using the X-ray diffractometer method (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 124-130 
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    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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    URL: http://dx.doi.org/10.1107/S002188988100890X
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    The use of cell and symmetry information for single-crystal orientation on diffractometers (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 117-123 
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    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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  • 151
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    Neutron powder diffraction of forsterite, Mg2SiO4: a comparison with single-crystal investigations (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 137-139 
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    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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  • 152
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    Adaptation of a Kratky camera to use with a one-dimensional position-sensitive detector (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 139-141 
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    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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  • 153
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    XPKFIT: peak separation with arbitrary relations among the component peaks (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 145-148 
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    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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  • 154
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    BLOKJE, a computer program to calculate the domain of an atom in a structure (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 151-153 
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    ISSN: 1600-5767
    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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  • 155
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    The use of continuous diffraction data as a phase constraint. I. One-dimensional theory (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 160-168 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    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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  • 156
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    A modified mirror monochromator for rotation photography of large-unit-cell crystals (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 658-661 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A double-mirror monochromator in which one of the mirrors is considerably longer than conventionally employed has been used to collect diffraction data from crystalline tobacco mosaic virus (TMV) protein (unit cell: 224 × 228 × 174 Å). Considerable improvements in speed of data collection are observed over both customary focusing optics and pinhole collimation. Quantitative comparisons are made of the quality of data collected from TMV protein by this method and by the use of nickel-filtered radiation.
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  • 157
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    Anisotropy in the flux-line lattice symmetry of a low-κ Type II superconductor (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 654-657 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Correlation between the symmetry of the two-dimensional flux-line lattice (FLL) and the real crystal lattice (CL) has been studied in a superconducting niobium sphere by means of small-angle neutron diffraction. A double-perfect-silicon-crystal diffractometer enabled precise determination of the three interfluxoid distances corresponding to the FLL basic cell. A systematic study of the anisotropic behavior was made as a function of temperature and magnetic field amplitude for fields parallel to a few high-symmetry CL axes in the (1{\bar 1}0) plane. In addition, at T = 4.30 K progressive deformation of the FLL was studied as the sample was rotated in the (1{\bar 1}0) and (100) planes. The FLL was found to be hexagonal only for fields parallel to the threefold CL axis. Twofold symmetry prevailed for other CL directions in these planes except near the fourfold axis, where either of two distorted triangular lattices existed, preserving the reflection symmetry in composite, but not individually. When compared to current models for fluxoid-CL interactions, the present results show that no theory predicts the observed behavior quantitatively under general conditions, but some models agree well for certain high-symmetry CL axes.
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  • 158
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    An error in several published tables of the multiplicities of powder reflexions (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 669-669 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Some multiplicities for the Laue class \bar 31m are not correct in several standard texts.
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    Determination of low-field critical parameters of superconducting niobium by small-angle neutron diffraction (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 650-653 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The double-perfect-crystal small-angle diffraction technique enables measurement of scattering angles to within an accuracy of 0.3′′ of arc. At a wavelength of 2.55 Å, this provides a resolution of 3 × 10−6 Å−1 in the scattering vector. This technique has been used to study the anisotropic behavior of the critical parameters B0 and Hc1, characteristic of the first-order magnetic phase transition which occurs in low-κ type II superconductors. Magnetic fields were applied parallel to several crystal axes in the (1{\bar 1}0) and (100) planes of a large single-crystal sphere of pure niobium, resulting in well defined flux-line lattices (FLL). Measurement of the FLL cell area in the intermediate, mixed-state-field region gives the equilibrium flux density B0, which results from an attractive interaction between fluxoids. In addition, field variation of the scattered neutron intensity allows measurement of the transition field between the mixed state and intermediate mixed state. This transition field is related to the lower critical field Hc1 and enables its determination to a precision of 0.2%. Data at T = 4.3 K display a small anisotropic effect of about 2% in B0 and 1% in Hc1. Although orientation effects of this magnitude are difficult to resolve by bulk measurements, the neutron data are in accord with magnetization data. The temperature dependence of these parameters is found to be in qualitative but not quantitative agreement with current theoretical models.
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  • 160
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    A computer program for determining multiplicities of powder reflections: a correction (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 669-669 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An amendment to a computer program for determining multiplicities of powder reflections [Rouse & Cooper (1977). J. Appl. Cryst. 10, 134–135] has been made to correct an error in the multiplicity values given for some reflections for space groups with {\bar 3}1m Laue symmetry, which exists in some of the standard texts.
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  • 161
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    Precision lattice parameter measurement by the X-ray divergent-beam technique (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 662-668 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A method is described for precision measurement of lattice parameters in cubic crystals, interplanar spacings and angles between crystallographic directions for single crystals of any system. The minimum measurable values of angle between crystallographic directions, Δd/d and Δa/a have been found to be ̃105 rad, ̃3 × 10−5, and ̃5 × 10−5, respectively.
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    Observation of lead Lα radiation from commercial X-ray tubes (1976)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 9 (1976), S. 370-370 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    World Directory of Crystallographers. Fifth Edition (1976)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 9 (1976), S. 371-371 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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  • 164
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    Crystal data for diphenylsilanediol, (C6H3)2Si(OH)2 (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 670-671 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The cell constants of recrystallized diphenylsilanediol were refined from precision powder data taken with Cr Kα1 (2.28962 Å): a = 14.493 (5); b = 15.012 (6); c = 9.897 (6) Å; α = 100.84 (9); β = 100.01 (5); γ = 120.77 (5); U = 1721.6 Å3; Z = 6; Dm (25°C) = 1.255 (3); Dx = 1.252 g cm−3.
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  • 165
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    Lattice parameter measurements in epitaxic layers (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 671-671 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Crystal growth and materials edited by E. Kaldis and H. J. Scheel (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 673-674 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    Simulation of photographs on a storage display. Application to X-ray topography and TEM (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 675-680 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The simulation of the photography remains the worst part in the calculation of transmission electron micrographs and X-ray topographs. Storage displays have been used to enhance this part of the process and the different possibilities of these screens studied. The quality of all simulations has been substantially increased by using these displays, which are now in common use.
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  • 168
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    High-resolution energy-dispersive diffraction using synchrotron radiation (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 684-687 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A high-resolution energy-dispersive diffractometer is described, which uses a synchrotron source and a scanning channel-cut silicon crystal. The technique is demonstrated with a powdered sample of BaTiO3 and analysis of the profiles demonstrates the anomalous particle-size effect reported by Anliker, Brugger & Känzig [Helv. Phys. Acta (1954), 27, 99–124].
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    Crystal mounter (1976)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 9 (1976), S. 416-416 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    International Tables for X-ray Crystallography (1976)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 9 (1976), S. 417-417 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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  • 171
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    Practical electron microscopy in materials science edited by J. W. Edington (1976)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 9 (1976), S. 418-418 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Applications of liquid crystals by G. Meier, E. Sackamann and J. G. Grabmaier (1976)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 9 (1976), S. 418-418 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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  • 173
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    Estimating unit cell volumes from powder diffraction data: the triclinic case (1976)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 9 (1976), S. 424-428 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: In the computer indexing of powder diffraction patterns, an advance estimate of the volume of the unit cell is extremely valuable. This paper describes a method for estimating it directly from powder-pattern data for the case of triclinic materials. The method involves an easily prepared graphical plot, the slope of which is proportional to the unit-cell volume. First, the diffraction lines are numbered consecutively, starting with the largest d value (N = 1). A plot is then made of 1/N versus d3. Theoretically, the resulting line has a slope of 3/(2πV) = 0.4775/V for triclinic compounds, where V is the unit-cell volume. Examination of the graphs plotted for a number of triclinic materials where the experimental data are of high quality shows that the slope consistently falls around 0.60/V. Hence, the volume of the unit cell and/or the calculated density can be estimated. In addition, this analysis gives a numerical measure of the fraction of possible diffraction lines actually observed.
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    A computer-controlled triple-axis neutron spectrometer with CAMAC interface (1976)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 9 (1976), S. 444-453 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A description is given of the computer-controlled triple-axis neutron spectrometer system installed at the PLUTO reactor at Harwell. Following the operation of the original system for several years a number of major improvements have been made which have resulted in a highly reliable system which provides the users with very powerful and extensive facilities. Following a general description of the modified spectrometer, details are given of the new computerized control system which utilizes a CAMAC modular interface and the functions of the various programs which are now available to the users are described.
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    Fundamentals of crystal growth 1 by F. Rosenberger (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 401-402 
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    The small-angle neutron scattering spectrometer at the University of Missouri research reactor (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 370-382 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    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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    A study of the ordered structures of the Au–Mn system by high-voltage–high-resolution electron microscopy. II. Two-dimensional antiphase structures based on the DO22 structure (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 392-400 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    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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  • 178
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    Comparison of two numerical methods for the integration of the Takagi–Taupin equations (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 432-436 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    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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  • 179
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    Dependence of cooling rate of SAXS spectra from a B2O3–PbO–Al2O3 glass (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 444-446 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    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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  • 180
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    Phase assignment to diffraction patterns based on the analytic properties of scattered fields applied to the structure of nerve myelin (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 455-461 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    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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  • 181
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    Crystal data for [2.1.2.1]paracyclophan C30H28 (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 465-465 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    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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  • 182
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    Diffraction from materials edited by L. H. Schwartz and J. B. Cohen (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 719-720 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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  • 183
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    Crystal growth 1977 edited by R. L. Parker, A. A. Chernov, G. W. Cullen and J. B. Mullin (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 720-720 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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  • 184
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    X-ray television area detectors for macromolecular structural studies with synchrotron radiation sources (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 1-9 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Two-dimensional X-ray diffraction patterns may be recorded quantitatively by means of X-ray-to-electron converters which are scanned in a television-type raster scan. Detectors of this type are capable of operating over the whole range of counting rates from very low to higher than those with which other types of converters can deal. The component parts of an X-ray television detector are examined and the limits to the precision of the measurements are analysed.
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  • 185
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    On the possibility of utilizing holographic schemes in X-ray microscopy (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 19-24 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: X-ray holography schemes are analyzed. It is shown that they have a very low aperture ratio, and this limits the size of objects from which a hologram can be recorded. It is indicated that holography schemes can be constructed on the basis of the methods of X-ray diffraction optics.
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  • 186
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    Report of Executive Committee for 1980 (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 491-491 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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  • 187
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    A method of determining cubic parameters suited to the conditions of high- and low-temperature powder diffractometry (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 5-14 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    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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  • 188
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    Diffraction line profiles and Scherrer constants for materials with cylindrical crystallites (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 20-26 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    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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  • 189
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    X-ray line profile analysis of deformed Al (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 35-38 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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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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  • 190
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    An improved EXAFS-function calculation procedure for materials with small interatomic separation (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 39-47 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    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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  • 191
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    An X-ray film powder profile refinement of the crystal structure of Ta5P3 (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 605-607 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    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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  • 192
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    The space group of γ-In2Se3 and γ1-(GaxIn1−x)2Se3: erratum (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 611-611 
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    Topics: Geosciences , Physics
    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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  • 193
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    Small-angle X-ray data processing for planar multilayered structures. I. Theory (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 42-48 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The Fourier transform values are obtained by multiplying the integrated intensities by the correction factor C(h). The problem of calculating the correction factor for biological specimens which have a multilayered structure is treated. Allowance is made for the transverse size of the specimen, the disorientation in the specimen (ω), the divergence of the X-ray beam (ε), the size of the repeating unit and the curvature of the sphere of reflection. The correction factor C(h) is given by C(h) = Ω[1 + 2γh2]1/2 exp (πδ2)exp (−Ω2[1 + 2γh2]), where γ = (ω2 + ε2)/2(Ω2d2) and where Ω is the diameter of the hth order disc when ω = ε = 0. The formula for C(h) applies to specimens which remain stationary during the X-ray experiment.
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  • 194
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    Pyroelectric temperature analysis as a method for study of ferroelectric transitions in polycrystalline materials (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 54-56 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The transition temperature of ferro- and antiferroelectric crystals can be simply determined by continuous pyroelectric temperature analysis (PTA) of unsintered pressed powder. In order to avoid excessive stored charge the samples were not previously treated by a polarizing electric field. Experiments performed with (NH4)2SO4, KH2PO4 and NH4H2PO4 showed the transition points with a precision of 1°C.
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  • 195
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    Five new polytypes and polytypic change in PbI2 (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 57-59 
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    Notes: Five new PbI2 polytypes, 8H(1232), 10H(11112112), 10H(112222), 22H[11(22)5] and 30R[111313]3, were solved by the X-ray diffraction method. It was found on polytypic change that (a) the 2H polytype is changed into various polytypes on heating at 130°C and most of these further change to 12R[13]3 on heating at 260°C; (b) the polytypes 4H, faulted 4H, 14H, 22H, 26H and 30R with layer structures similar to the 12R[13]3 are fairly stable at high temperatures; (c) the 2H-30R [111313]3 transformation occurs reversibly.
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  • 196
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    Orientations mutuelles observées sur des cristaux d'hématite (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 66-69 
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    Topics: Geosciences , Physics
    Notes: The reactivity of hematite depends among other factors on the morphology of the crystal. The choice of the orientation of the reference axes has been made with the help of stereographic projection combined with the morphology of the etch figures on the different faces of the crystal. That the most stable face of a crystal corresponds to the composition plane is shown for crystals of hematite from Elba.
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  • 197
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    Etude des défauts dans des monocristaux naturels de béryl. I. Observations des dislocations (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 70-77 
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    Notes: The lattice defects of beryl single crystals from Brazil and Madagascar have been studied by X-ray topography. Two types of linear defects are observed: channels and grown-in dislocations. Slip systems and Burgers-vector moduli are determined. Some calculations of directions of minimum dislocation energy are given and they are in quite good agreement with the observations.
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    FN: A criterion for rating powder diffraction patterns and evaluating the reliability of powder-pattern indexing (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 60-65 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: At present, over 30 000 powder diffraction patterns are available as references. It is proposed that the patterns on file as well as new patterns submitted for publication be assigned quantitative quality factors. A simple-to-use figure of merit, FN, covering both accuracy in the measurement of the positions of the diffraction lines and completeness of the pattern, has been derived: FN = (1/|{\bar \Delta 2 \theta}|) (N/Nposs), where Nposs is the number of independent diffraction lines possible up to the Nth observed line and |{\bar \Delta 2 \theta}| is the average absolute discrepancy between observed and calculated 2θ values. This figure of merit provides a rapid evaluation of powder patterns, in much the same way as the R factor provides a rating for single-crystal structure determinations. This figure of merit also provides a means to assess the reliability of a unit derived solely from powder data. At present FN ranking scheme is shown to be superior to de Wolff's M20 for ranking patterns. It is recommended that use of the latter be discontinued for that purpose. Guidelines are given on the use and implementation of the FN rating of powder diffraction patterns.
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    X-ray line-profile analysis. I. A method for unfolding diffraction profiles (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 184-190 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A new method for unfolding X-ray diffraction profiles is reported. The procedure is based on the minimization of an economical function defined as the sum of the squared relative differences between the experimental function and a calculated profile. The latter is numerically computed from the convolution equation by fitting the pure diffraction profile with a damped polynomial. The influence of the truncation and the width of the instrumental function is studied; some results are given concerning the evaluation of a constant background for both the experimental and instrumental functions and its influence on the precision of the results. Finally, the perturbation produced by the simulation of statistical noise is discussed.
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  • 200
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    Données cristallo-chimiques sur le tétrapolyphosphate mixte de germanium et ammonium: (NH4)2GeP4O13 (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 200-200 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The tetrapolyphosphate (NH4)2GeP4O13 is triclinic (P{\bar 1}), with a unit cell: a = 15.08 (1), b = 7.763 (5), c = 4.914 (5) Å, β = 98.18 (1), β = 96.53 (1), γ = 84.04 (1)° and Z = 2. This salt is isotypic with the corresponding salt of silicon: (NH4)2SiP4O13, previously described by the author.
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