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  • Articles  (13,413)
  • International Union of Crystallography (IUCr)
  • Public Library of Science
  • 1990-1994  (7,163)
  • 1985-1989  (6,250)
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  • Articles  (13,413)
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  • 101
    Electronic Resource
    Electronic Resource
    Determination of single-crystal elastic constants from a cubic polycrystalline aggregate (1985)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 18 (1985), S. 513-518 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A method for determining cubic stiffness constants from polcrystalline Young's modulus and X-ray elastic constants is described. The relations used among these elastic constants are those based on Kröner's quasiisotropic model. The X-ray elastic constants required [S1(hkl)] are obtained by measuring various (hkl) d spacings of a stressed specimen under symmetric θ–2θ scan mode. An application to an Fe–31Ni alloy has given the results: C11 = 1.47, C12 = 1.05 and C44 = 1.24 × 1011 Pa.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889885010809
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  • 102
    Electronic Resource
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    Observations of growth defects in berlinite by high-temperature X-ray topography (1985)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 18 (1985), S. 533-534 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Growth defects in a synthetic berlinite sample were studied at high temperature (300–500 K) by X-ray topography. Preliminary observations of contrast changes with temperature are reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889885010834
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  • 103
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    Structural information on proteins obtainable from small-angle X-ray scattering with heavy-atom labeling. Application to solubilized bacteriorhodopsin (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 355-362 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The heavy-atom labeling method is applied to small-angle X-ray scattering (SAXS) based on contrast variation in order to derive information on the inner structure of proteins. The formulation of the contrast variation is extended to express explicitly the contribution of the bound heavy atoms to SAXS. The present method reveals two important features concerning bound heavy atoms, namely their number and their distribution. The application of this method to solubilized bacteriorhodopsin (bR) with iodination revealed the following characteristics of structure. The number of bound iodine atoms is 20, indicating that the solubilized bR is composed of a trimer of bR molecules. The mean square distance between the iodine position and the center of the trimer is about 1660 Å2, indicating that the most active tyrosine residues are located near the outer rim of a bR trimer. The distribution of iodine atoms is symmetric about the center.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S002188988800319X
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  • 104
    Electronic Resource
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    Feasibility of running the dynamical HREM multislice program on a 16-bit minicomputer (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 369-371 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The program of multislice calculations written by Ishizuka [User's Manual of Multislice and Image-Simulation Programs (1982). Center for Solid-State Science, Arizona State University, USA] for large central computers has been successfully transferred to the 16-bit PDP-11/24 minicomputer, without disturbing its features and capacities. The structural modifications of the transferred program lead to a great reduction of the calculation time for running on the PDP-11/24. The function of halftone output of calculated diffraction patterns has been developed and added to the package. This package proves to be especially effective in image simulations for complex structures (medium or large unit cells) on a minicomputer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888002304
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  • 105
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    Crystallographers (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 380-381 
    Details
    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/S0021889888005655
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  • 106
    Electronic Resource
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    Computer program for calculation of interface structures (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 381-382 
    Details
    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/S0021889888003656
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  • 107
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    New Commercial Products (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 382-382 
    Details
    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/S0021889888099728
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  • 108
    Electronic Resource
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    Quartz by M. O'Donohue (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 384-384 
    Details
    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/S0021889888001244
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  • 109
    Electronic Resource
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    Synchrotron Laue topography studies of pseudo-hexagonal twinning (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 406-415 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Pseudo-hexagonally twinned orthorhombic crystals generally exhibit three domain variants related by mirror planes or (approximately) by 120° rotations. The reciprocal lattices of the three domains coincide partially. Those reciprocal-lattice points hkl with h + k = 2N coincide or are split depending upon the deviation of the a:b ratio from orthohexagonality (i.e. a:b = tan 60°). With (white-beam) synchrotron radiation these domains are simultaneously imaged by Laue X-ray topography for these reflections. Lattice points hkl with h + k = 2N + 1 are `single' and only one of the three domain variants is imaged in such reflections. Two examples of these twins are presented, LiNH4SO4 and (NH4)2SO4. In the former case the lattice is closer to the ideal ratio a:b = tan 60° than the latter. These two cases are contrasted. Both materials are subject to some extent to radiation damage in the synchrotron beam.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S002188988800408X
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  • 110
    Electronic Resource
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    Bimodal distributions of profile-broadening effects in Rietveld refinement (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 416-425 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: It is demonstrated with computer simulations that a bimodal distribution (narrow and broad) of reflection profile broadening effects, such as crystallite size and microstrain, can lead to several spurious results when the profiles are modeled by single pseudo-Voigt functions in Rietveld refinement (RR), e.g. mixing parameter η 〉 1 (`super-Lorentzian'), a few observed data points lying consistently above the calculated peak maxima for some reflections, misrepresentation of the background level and shape, and in special cases well defined small observed peaks not seen in the calculated pattern as though they belonged to an additional minor phase. With a bimodal model (two pseudo-Voigt functions) the RR's accurately returned the profile, mixing, and background parameters used in the data synthesis both without and with counting statistical fluctuations simulated in the data. The RR method thus demonstrates remarkable ability to sort out complex specimen characteristics when accurate modeling functions are used.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888004091
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  • 111
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    Synchrotron X-ray and neutron powder diffraction studies of the structure of α-CrPO4 (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 452-457 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The crystal structure of α-CrPO4, previously solved from high-resolution synchrotron powder X-ray data, has been refined by the Rietveld method. The peak shape variation is well fitted by a convolution of Gaussian and Lorentzian terms, which incorporate both instrumental and sample-broadening contributions. The structure has also been refined using medium-resolution neutron diffraction data, and the results of the two experiments are compared with a reported single-crystal study. The three sets of coordinates are found to be in good agreement, demonstrating the potential of structure determination and refinement using powder data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888004625
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  • 112
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    Crystallographers (1985)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 18 (1985), S. 544-544 
    Details
    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/S0021889885010913
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  • 113
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    Crystal data for 1.3-dibromo-5-methylbenzene at 293 K (1985)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 18 (1985), S. 542-542 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The title compound C7H6Br2 (also called 3,5-dibromotoluene) is orthorhombic, space group P212121 with a = 14.426(2), b = 13.636(2), c = 4.076(1) Å, V = 801.8(3) Å3, Z = 4, Dx = 2.071 Mg m−3. The space group and preliminary cell parameters have been determined by single-crystal diffraction methods (Bragg, Weissenberg and precession patterns). The cell dimensions have been refined by least squares from accurate powder diffractometer data recorded at T = 293(1) K (quartz as internal standard, Cu Kα1−Kα2 correction so that λ = 1.54056 Å). The indexed powder data are given. No phase transition is detected between 123 K and the melting point 311.1(2) K (differential scanning calorimetry and Guinier–Lenné analysis). The results show that 1,3-dibromo-5-methylbenzene is isomorphous with 1,3,5-trichlorobenzene and 1,3,5-tribromobenzene. The JCPDS Diffraction File No. For C7H6Br2 is 36-1991.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889885010895
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  • 114
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    Effect of divergence and receiving slit dimensions on peak profile parameters in Rietveld analysis of X-ray diffractometer data (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 398-405 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A range of `normal' divergence (0.25, 1.0°) and receiving (0.1, 0.2, 0.4 mm) slit dimensions has been used to determine their effect on the peak profile parameters obtained by Rietveld analysis of X-ray powder diffraction data from a conventional X-ray source. The instrument is a standard Bragg–Brentano diffractometer equipped with a diffracted-beam monochromator and Soller slits. The instrumental profile characteristics are provided by a sample of coarsely crystalline Si, and the effects of small particle size and isotropic strain by fluorite, CaF2. Results are discussed for refinements of the full diffraction patterns (24 to 140°), and of the individual peaks at 28, 47 and 88° in each pattern. The use of a wide receiving slit aperture (i.e. 0.4 vs 0.1 mm) provides (i) increased peak intensities, (ii) much improved values of the Rietveld agreement indices (especially at low angles), (iii) slightly more Gaussian peak shapes, and (iv) slightly wider peaks. A wider divergence slit (i.e. 1.0 vs 0.25°) has only a small effect on the refinement results. The Voigt and pseudo-Voigt peak shape models are seriously deficient for low-angle peaks when axial divergence is larger than about 2°, but are otherwise satisfactory. The CaF2 peaks are wider and more Lorentzian in character (at high angles) than those obtained for Si, owing to the presence of very small (350 Å) and strained crystals; in this case, the peak shape/width characteristics can be adequately modelled at all diffraction angles, regardless of axial divergence. Quantitative information about crystal size and strain can be extracted from the CaF2 pattern by direct incorporation of the instrumental profile into the parameters of the Voigt function during Rietveld refinement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888003474
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  • 115
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    Instrumental resolution effects in small-angle neutron scattering (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 438-451 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Experimentally measured scattering data differ from theoretical curves because of departures from point geometry in a real instrument. In a small-angle neutron scattering (SANS) instrument, there are essentially three contributions to the smearing of an ideal curve: (1) the finite divergence of the beam, (2) the finite resolution of the detector, and (3) the poly chromatic nature of the beam. Where the scattering is azimuthally symmetric about the incident beam, indirect Fourier transform (IFT) methods may be used not only to smear an ideal scattering curve, but also to desmear an observed pattern. For experiments where the assumption of azimuthal symmetry cannot be made, alternative procedures based on Monte Carlo (MC) techniques have been developed which simulate the smearing of a given theoretical scattering function. This procedure permits the evaluation of smearing effects in anisotropic systems. Both IFT and MC procedures are illustrated with a range of applications from data taken on the 30 m SANS facility at Oak Ridge National Laboratory. It is shown that for experiments with scattering dimensions 〈 200 Å smearing effects are small (〈 5%) and that dimensions up to ̃1200 Å may be accurately resolved after proper evaluation of resolution effects. The procedures described may also be extended to include small-angle X-ray scattering, and an example of one such application is given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888004273
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  • 116
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    Integration of single-crystal reflections using area multidetectors (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 471-478 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The development of multidetectors for use in X-ray and neutron scattering experiments has created an interest in methods for integrating Bragg peaks in three-dimensional data arrays representing intensity scattered from single crystals. A method of using a priori information, extracted from the strongest peaks, to obtain statistically optimum results has been developed at the Institut Laue–Langevin (ILL), Grenoble. The method is outlined in this paper and results of its application to neutron diffraction are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888005400
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  • 117
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    Principles of differential energy-dispersive X-ray spectroscopy (DEDXS) (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 496-503 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Conventional methods and problems of differential X-ray spectroscopy using characteristic radiation are briefly described. The principles of energy-dispersive methods of differential spectroscopy are then described, covering both high- and low-resolution systems. By using digital electronics to control the modulation, errors associated with timing are reduced to well below those associated with the random nature of X-ray emission. By delaying demodulation until the final counting stage, thus using only one chain of electronic processors, errors associated with two chains of different characteristics are eliminated. Stability of the source is no longer an important criterion and the method is ideally suited for use with synchrotron radiation sources where beam intensity decays with a half-life of a few hours. It is also possible to derive the modulation cycles from the oscillator that controls the electron bunches in the storage ring, thereby making possible time-resolved and phase-sensitive studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888005643
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  • 118
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    Use of a shared-memory parallel processor in the restrained least-squares procedure of Hendrickson and Konnert (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 512-515 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The restrained least-squares refinement procedure PROLSQ of Hendrickson & Konnert [Hendrickson (1985). Methods in Enzymology, Vol. 115, edited by H.W. Wyckoff, C. H.W. Hirs & S.N. Timasheff, pp. 252–270. Orlando: Academic Press] has been implemented on a 30-processor Sequent Balance 21000 shared-memory parallel processor. The adaptation of PROLSQ to a general-purpose parallel computer offers the potential of performance increase as the physical limits are approached in traditional sequential and vector processing hardware.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888005813
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  • 119
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    Interface roughness and period variations in MQW structures determined by X-ray diffraction (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 524-529 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A method for estimating the interface widths in multiple quantum well (MQW) structures is described. Generally it has been assumed that the average interface shapes on each side of a quantum well are the same, yet there is no reason to assume that this is correct. The method presented here can predict the interface profile on both sides of a quantum well and therefore detect the presence of any asymmetry. The results are compared with the more familiar predictive Fourier transform approach and qualitative agreement is observed, although the latter cannot predict any asymmetry. Deducing the interface width from the predictive Fourier transform method can be difficult because of series termination effects and could possibly be misleading if insufficient satellites are measured. The limitations are essentially by-passed with the described approach. A simple method for deriving period variations is also given and in the example presented this amounts to about two monolayers. The interface widths in this example are 6.5 and 5.4 monolayers and these best-fit values give an R-factor just above that which could be expected from the data. Also the fit for two similarly graded interfaces results in a significant worsening in the agreement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888006569
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  • 120
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    Scattering exponents for polydisperse surface and mass fractals (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 25-27 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Scattering exponents are discussed for systems of power-law polydisperse surface and mass fractals. It is found that the scattering exponent for power-law polydisperse mass fractals lies on the interval [0, d] and always depends on the mass fractal dimension. The scattering exponent for power-law polydisperse surface fractals lies on [0, d + 1] and is independent of the surface fractal dimension for a large range of the polydispersity exponent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889886090052
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  • 121
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    A real-time interactive graphics program to determine crystal orientation for the analysis of oscillation diffraction photographs (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 28-33 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: This paper describes a powerful preliminary to various least-squares programs for finding the exact crystal orientation for the oscillation method. It is well suited to cases of large initial misorientation. It uses the real-time rotation and clipping capabilities of the high-performance graphics system PS300 from Evans & Sutherland. A program has been written that performs a geometrical inversion of reciprocal space through its origin and manipulates this transformed image in place of the direct one. The Ewald sphere is thus transformed into a plane that can be superimposed on the film. The crossing of any reciprocal-lattice point through the Ewald sphere is then replaced by the crossing of its transform through the film plane. Clipping allows elimination of all the points too far away from this plane, i.e. those that are not in a diffraction condition. Determination of the correct orientation is achieved by superimposing the inverted reciprocal-lattice image on the corresponding transformed image of the observed film.
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    URL: http://dx.doi.org/10.1107/S0021889886090040
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  • 122
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    Systematic errors in precision lattice-parameter determination of single crystals caused by asymmetric line profiles (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 34-38 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The convolution of the various contributions to X-ray intensity distribution curves measured in lattice-parameter determination leads to peak shifts and, hence, to systematic errors in the case that at least one of the contributing curves is asymmetric. For perfect crystals, depending on the collimator divergence, this effect may reach the order of magnitude of the refraction correction. It is caused by the asymmetry of the spectral distribution curve, which includes intrinsic asymmetry, dispersion and angle dependence of intensity (ADI). For imperfect crystals characterized by orientation and interplanar-spacing distributions, the distribution curves should be measured in order to correct accurately the peak shift. Examples of simulation calculations are given for Si, Cu Kα1, Bond method for various reflections of perfect crystals and for crystals having orientation distributions, 444 reflection.
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    URL: http://dx.doi.org/10.1107/S0021889886090039
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  • 123
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    Accuracy and resolution in small-angle crystallographic analyses. A comparison with solution scattering studies (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 51-60 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: This paper is an extension of the preceding one and deals with the problem of assessing the potential accuracy of low-resolution crystallographic analyses restricted to the same angular range as solution scattering studies. The mathematical treatment is very similar in the two papers; similarly, the final result takes the form of a curve relating the normalized variances of the positional and chromatic structure parameters. In the absence of `small-angle' data – these are utterly disregarded in routine protein crystallographic analyses – an ideal experiment performed on a low-density serum lipoprotein, under conditions similar to those that prevailed in the experimental study of methionyl t-RNA synthetase, is used as an illustration. The potential accuracy estimated for this putative crystallographic analysis is found to be quite close to that assessed for the solution scattering experiment. In the case of protein crystallographic analyses, the projection information associated with the `small-angle' reflections is estimated and it is shown that it amounts to a substantial fraction of the whole of the experimental information. More precisely, the average information per reflection is almost 40 times larger for the `small-angle' than for the other reflections. The conclusion is reached that 'small-angle' reflections should be involved in protein crystallographic analyses and it is suggested that in the early stage of the phasing process `small-angle' crystallographic data and solution scattering experiments be combined together to locate and orient the molecule(s) in the cell and to draw the molecular envelope.
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    URL: http://dx.doi.org/10.1107/S0021889886090015
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  • 124
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    Information content and retrieval in solution scattering studies. II. Evaluation of accuracy and resolution (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 39-50 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The aim of this paper is to assess the potential accuracy of structure analyses based upon solution X-ray scattering experiments, before the structure problem is solved. In other words, an algorithm is sought expressing accuracy in terms of the experimental observations and associated errors, independently of the value of the structure parameters. The mathematical treatment involves five steps: (a) Data reduction, namely the definition in experimental space of the degrees of freedom of the problem and the determination of their probability law. (b) Choice of representation of the structure consistent with the coarse resolution of solution scattering experiments; a set of sharp pseudo-atoms is adopted, so that the degrees of freedom in real space are the position and electron density of each pseudo-atom. (c) Introduction to a `virtual experiment' defined by a noise distorting the structure parameters, and determination of the corresponding probability law in the experimental space. (d) Comparison of the real and the virtual experiments, or more precisely of the probability laws of the degrees of freedom in experimental space, yielding a relation between the variances of the position and electron density uncertainties, the number of the pseudo-atoms and the value of the structure parameters. (e) Attenuation of the structure dependence via the introduction of a hypothesis of quasi-spherical symmetry, whose effect is to reduce the expression of the variances to a function of the experimental observations, independent of the knowledge of the structure of the particle. This analysis is applied to solution X-ray scattering experiments at variable contrast, interpreted within the framework of the invariant volume hypothesis. The final result takes the form of a curve relating the variances of the position and electron density uncertainties, divided by the number of pseudo-atoms. The example of a low-density serum lipoprotein is used to illustrate these results.
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    Powder diffraction peak shapes. Parameterization of the pseudo-Voigt as a Voigt function (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 63-64 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The Voigt function is now recognized to be one of the best mathematical descriptions of the symmetrical component of the peak shape in constant-wavelength X-ray and neutron powder diffraction. The simpler pseudo-Voigt function has been used previously to provide an empirical fit to observed peak shapes. In this paper, a parameterization of this function is obtained to make it, to a very good approximation, equivalent to a Voigt function, and, additionally, it is described by the half-width parameters of the Gaussian and Lorentzian components of that Voigt function. This new construction allows for greater flexibility in peak-shape description and, in particular, allows for a more straightforward convolution of additional functional contributions into the `Voigt' component of a peak shape description.
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    Strategies for collecting screen-less oscillation data (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 61-62 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Screen-less oscillation photography is the method of choice for recording three-dimensional X-ray diffraction data for crystals of biological macromolecules. The geometry of an oscillation camera is extremely simple. However, the manner in which the reciprocal lattice is recorded in any experiment is fairly complex. This depends on the Laue symmetry of the reciprocal lattice, the lattice type, the orientation of the crystal on the camera and to a lesser extent on the unit-cell dimensions. Exploring the relative efficiency of collecting X-ray diffraction data for different crystal orientations prior to data collection might reduce the number of films required to record most of the unique data and the consequent amount of time required for processing these films. Here algorithms are presented suitable for this purpose and results are reported for the 11 Laue groups, different lattice types and crystal orientations often employed in data collection.
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    SANS studies of the microstructure of a three-componnent microemulsion (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 835-839 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Small-angle neutron scattering measurements have been performed on a three-component microemulsion system consisting of water, hexane and didodecyl-dimethylammonium bromide. For a water-to-surfactant weight ratio of 0.95 and less than 5 wt% surfactant, these measurements are best fit by a model with a Gaussian size distribution of spherical water droplets in hexane. The average water core radius is determined to be about 2.9 nm. On addition of water while the same water-to-surfactant ratio is maintained, there is some evidence that the basic unit of the microstructure remains a sphere with the same radius. The interaction between the spheres is found to be attractive, and the spheres may be connected for volume fractions of water larger than 5%.
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    SANS study of sintering of rough surfaces (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 864-869 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Small-angle scattering has been used to follow the heat-induced smoothing of rough fumed silica particles by viscous sintering. When analyzed by a fractal surface model, the surfaces evolved from a fractal dimension of 2.5–2.7 to 2.0. The specific surface area σ(r) for a given resolution r could be described by the simple law σ(r) = σ0(r/r*)2−D, where σ0 is the specific surface area for smooth particles and r* is a characteristic length that is the same for all the fumed silicas studied and is comparable to the primary particle size. This is the first indication of a universal relation between fractal surfaces, albeit within a closely related class of materials.
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    Cell dynamical system study of phase separation dynamics (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 883-885 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A cell dynamical system (CDS) is defined by a map which takes a configuration on a lattice at a time t to a configuration at time t + 1. Phase-ordering dynamics, block copolymers etc. have been modeled in terms of CDS. With the phase-ordering dynamics model, the scaling exponent (and the universal function) for the form factor in the scaling regime and the effect of noise on these have been studied. It is clearly observed that, for the ordering process in the (critically quenched) conserved order parameter case, the scaling exponent crosses over from ̃0.28 to ̃0.33. This crossover is delayed with the introduction of noise, with larger amplitudes of noise causing a greater delay.
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    High-resolution synchrotron X-ray powder diffraction with a linear position-sensitive detector (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 905-910 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: X-ray synchrotron powder data were collected from a capillary sample of a small-molecule organic peptide compound, glycylglycine (NH2CH2CONHCH2COOH) by step-scanning at 1° intervals with a linear position-sensitive detector covering an angular range of 2.7° in order to test the feasibility of recording a high-resolution pattern and using the data for Rietveld analysis. Appropriate corrections for detector linearity and position were implemented, and comparison with a diagram recorded with a single scintillation detector and a crystal analyser system showed similar quality for the two sets of data. A detailed comparison of the refined atomic coordinates and those of an earlier X-ray single-crystal study showed the estimated standard deviations to be significantly underestimated in both refinements. A linear detector should be particularly useful for small samples and capillary specimens of moderately absorbing materials.
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    On the calculation of diffracted intensities from SiC crystals undergoing 2H to 6H transformation by the layer displacement mechanism (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 935-942 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Computer simulation of 2H to 6H transformation by non-random insertion of layer displacement faults in a random space and time sequence has been performed. The model employed by Pandey, Lele & Krishna [Proc. R. Soc. London Ser. A, (1980), 369, 435–477], which is based on the sequential insertion of layer displacement faults, allows faulting of one-third of the total number of layers on completion of the transformation. The results of the simulation show that the transformation gets arrested because of the formation of interfaces by the impingement of independently formed 6H regions and that the fraction of faulted layers which can be inserted is just 0.276. It is shown that these interfaces are such that they do not lead to any broadening of the 6H reflections common with 2H. While this is in agreement with the theoretical predictions of Pandey et al., the diffuse intensity distribution calculated for the arrested state shows significant departures.
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    Einfluss der Valenzelektronenkonzentration auf die Bildung der Phasen vom Ni2In-Strukturtyp am Beispiel der ternären Verbindungen Mn2Ga0.5As0.5(m),Fe3GaAs und Co2Ga0.5As0.5 (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 80-85 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The structures of the metastable phase Mn2Ga0.5As0.5 (m) and the stable phases Fe3GaAs and Co2Ga0.5As0.5 are isotypic with Ni2In. X-ray powder diffraction data are reported. Lattice constants and macroscopic densities were measured in the entire range of homogeneity. Crystal chemical parameters of these ternary phases and of the quasi-homologous isovalent phases are compared and discussed from the point of view of the valence-electron concentration and of the number of atoms in the unit cell. It is concluded that the valence-electron concentration is a very important but not a sufficient energetic factor for the stability of phases with the Ni2In structure.
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    Lattice thermal expansion behaviour of spinel HgCr2Se4 (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 86-89 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An accurate value of the lattice parameter of the spinel ferromagnetic semiconductor HgCr2Se4 has been determined at different temperatures, ranging from 298 to 770 K, by X-ray powder diffraction. The data have been used to evaluate the coefficient of thermal expansion, α, at various temperatures. The temperature dependence of the coefficient of expansion can be represented by the equation α = 10.059 × 10−6 − 1.862 × 10−8 T + 3.017 × 10−11 T2, where T is the temperature in K. The diffraction pattern of HgCr2Se4, obtained at 785(5) K, was completely different from that at room temperature. The high-temperature phase persisted up to 900 K, and above this the compound decomposed. Furthermore, the new phase was retained when the sample was cooled from 900 K to room temperature. These results suggest an irreversible structural phase transformation in HgCr2Se4 at 785 K. An attempt is made to explain this interesting high-temperature thermal behaviour of HgCr2Se4 in relation to its structure and other physical properties.
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    CAMAL – a new component of the Cambridge Structural Database software system (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 90-91 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The efficient use of crystallographic databases necessitates the use of statistical techniques. CAMAL is a library of Fortran subroutines for performing simple and multivariate statistical calculations. The library is intended for use with the Cambridge Structural Database and is distributed by the Cambridge Crystallographic Data Centre.
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    Interactive graphics for rapid indexing of oscillation films from large unit cells (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 101-104 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An interactive graphics program for the Evans & Sutherland PS330 has been written to display and index screenless X-ray oscillation films from macromolecular crystals with unit-cell edges of at least 500 Å. ALIGN, a Fortran program which works in conjunction with M. G. Rossmann's program OSCMGR, accurately displays densitometered reflection intensities, provides the required transformation between predicted and observed reflection coordinates, and is useful in determining crystal mosaicity and detecting unit-cell changes.
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    Stroboscopic X-ray topography of quartz resonators (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 967-971 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Stroboscopic X-ray topography has been performed to observe the different states of acoustic vibrations in quartz resonators with a time resolution of 1 ns. These experiments have been made at LURE (Orsay, France) using the pulsed light delivered by the DCI storage ring. The studied resonators have shown that the vibration is affected by the nature, the density and the distribution of the defects.
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    Accurate determination of lattice parameters from XRD oscillation photographs (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 991-991 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    QUIDCRYST-87, a software package for X-ray data collection using a two-circle computer-controlled diffractometer (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 993-993 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    MISSYM1.1 – a flexible new release (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 983-984 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Version 1.1 of MISSYM is now available and the following new features have been added: a HELP facility to guide and caution the user; the input of a distance tolerance for axes and planes, and a separate tolerance for inversion centers and translations; the possibility of flagging atomic positions as `possibly disordered'; the possibility of allowing for errors in assigning chemical types; the possibility to extract the symmetry for a single atom type; the option to run from sensible default values. This version is more flexible than, but not quite as fast as, the original. Only one-third of structures require the full application of MISSYM because simple conditions, simultaneously satisfied by about two-thirds of the structures published recently, rule out the possibility of extra symmetry in the model. The existence of an efficient computer program for flagging the cases of overlooked symmetry should not give a false sense of security or be used to justify short cuts in the preliminary study of crystal symmetry.
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    High-reflectivity multilayer monochromators for neutrons (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 123-130 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Ni–Ti multilayers were fabricated in an r.f. sputtering system. Reflectivities of the multilayers were measured with a neutron beam having a beam divergence of 0.29 mrad and a beam width of 0.32 mm. Reflectivities of the multilayers and their diffraction properties were compared with results obtained from the dynamical theory for perfect multilayers. Attempts were then made to minimize the imperfections in multilayers and obtain good-reflectivity multilayers with small d spacings. Multilayers with d spacings from 60 Å up could be fabricated with reflectivities between 0.95 and 1.00.
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    The determination of molecular orientation: an efficient reciprocal-space algorithm for the small computer (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 131-133 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A rotation function is formulated in terms of a Fourier–Bessel-series expansion of the Patterson coefficients of the search model. The function provides an efficient algorithm for performing rotational analyses of small molecules on computers with limited memory and storage requirements.
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    Post-refinement of oscillation diffraction data collected at a synchrotron radiation source (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 134-139 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: `Post-refinement' is a technique used to compare the intensity of partially recorded reflections on oscillation photographs with their full intensity observed elsewhere on the same or a different film. A reflection's partiality depends on crystal orientation, crystal cell dimension and crystal mosaicity, and post-refinement is a very sensitive tool for the refinement of these parameters. A previous paper [Rossmann, Leslie, Abdel-Meguid & Tsukihara (1979). J. Appl. Cryst. 12, 570–581] describes how post-refinement can be applied to data derived from a set of oscillation films. In this paper the technique has been extended to the refinement of anisotropic beam divergence and wavelength dispersion as is normally found on synchrotron sources. In an example it is shown that post-refinement is sufficiently sensitive to detect small wavelength variations due to changes in temperature of the monochromating crystal.
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    Identification of Burgers vectors along 〈111〉 in In-doped GaAs, by X-ray transmission topography and image simulation (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 140-141 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Long dislocations with Burgers vectors along 〈111〉 are unusual in f.c.c. lattices. X-ray topographs have been obtained of as-grown GaAs crystals doped with 1020 atoms cm−3 of In, where the usual extinction criterion g.b = 0 leads to this type of defect. However, for several g satisfying the condition g.b = 0 with b = a [111], the images of these dislocations were still clearly visible. Comparison between experimental and computer-simulated X-ray topographic sections of these defects confirms the existence of Burgers vectors along 〈111〉.
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    Crystal data for 1-4-epoxy-4-[(4-nitrophenyl)methyl]-1-phenyl-1H-2,3-benzodioxepin-5(4H)-one (C22H15NO6) and 1,4-epoxy-4-[(4-bromophenyl)methyl]-1-phenyl-1H-2,3-benzodioxepin-5(4H)-one (C22H15BrO4) (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 142-142 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The indexed X-ray diffraction powder data of 1,4-epoxy-4-[(4-nitrophenyl)methyl]-1-phenyl-1H-2,3-benzodioxepin-5(4H)-one (OZONO, C22H15NO6) and 1,4-epoxy-4-[(4-bromophenyl)methyl]-1-phenyl-1H-2,3-benzodioxepin-5(4H)-one (OZOBR, C22H15BrO4) are reported. OZONO and OZOBR crystallize in the monoclinic space groups P21/c and P21/a, respectively. The cell constants are a = 8.200 (4), b = 14.574 (6), c = 15.908 (7) Å, β = 100.30 (3)°, V = 1870.5 Å3, Dm = 1.36 (1), Dx = 1.38 Mg m−3 for OZONO and a = 12.217 (5), b = 8.945 (2), c = 17.062 (5) Å, β = 96.85 (2)°, V = 1851.2 Å3, Dm = 1.49 (1), Dx = 1.52 Mg m−3 for OZOBR. The quantitative figures of merit (FN) are F20 = 62(0.007, 48) and F26 = 28(0.016, 58) deg−1, respectively. The JCPDS Diffraction File No. for OZONO is 36-1988 and for OZOBR 36-1989.
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    A comparison of the source emissivity distributions for two standard X-ray tubes (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 143-143 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Phase separation in glass edited by O. V. Mazurin and E. A. Porai-Koshits (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 144-144 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Easy and economic ways of handling air-sensitive crystals for X-ray diffraction studies (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 182-183 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Easy and convenient techniques have been developed to handle air-sensitive compounds in terms of measuring their single-crystal X-ray diffraction intensities. These methods have also been fruitfully applied in collecting X-ray data of several highly air-sensitive inorganic and organometallic compounds without using a cold stream of nitrogen.
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    Nominations for the Ewald Prize (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 187-187 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    A high-resolution diffuse X-ray scattering study of defects in dislocation-free silicon crystals grown by the float-zone method and comparison with Czochralski-grown crystals (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 209-215 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Point-defect aggregates in (111) dislocation-free silicon single crystals grown by the float-zone (FZ) method have been studied by diffuse X-ray scattering (DXS) and compared with those in the Czochralski-grown (CZ) crystals. A two-axis X-ray diffractometer was used. It employs three monochromators in (+, −, −) setting to obtain a highly collimated and monochromatic Mo Kα1 beam. DXS measurements were made around the 111 reciprocal-lattice point (r.l.p.) with K* along ±[111] and ±[01{\bar 1}]; K is the vector which joins the elemental volume of the reciprocal space under investigation to the nearest r.l.p. For FZ crystals for a given K* the DXS intensity was higher for θ 〈 θB in comparison with that for θ 〉 θB showing that the anisotropy (DXS Iθ 〉 θB − DXS Iθ 〈 θB) is negative, as expected for vacancy clusters. For CZ crystals the anisotropy was positive, owing to the presence of interstitial clusters. The magnitude of anisotropy in the FZ crystals was smaller than that observed in the CZ crystals. The DXS intensity varies approximately as K−2 near Bragg peaks (Huang scattering) and as K*−4 (Stokes–Wilson scattering) away from it. From the K* values where the changeover from Huang to Stokes–Wilson scattering takes place the size of the clusters assumed to be the origin of the observed DXS is estimated as ̃2 × 10−4 and 2.6 × 10−3 mm for FZ and ̃5.5 × 10−4 and 3 × 10−3 mm for CZ crystals. The experimental data were compared with theoretically calculated DXS distributions assuming the defects to be dislocation loops. The number of point defects in a loop has been estimated.
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    The influence of texture on the radial distribution function of solid carbons (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 205-208 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The effect of texture on the interpretation of the classical radial distribution function (RDF) is studied. A model of axial texture is presented which enables the calculation of the effect for individual interatomic distances and an analysis of the effect on the global RDF. The example shows that the shift of the RDF closest-neighbour peak position can be as large as 0.06 Å.
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    On the selection of measurement directions in second-rank tensor (e.g. elastic strain) determination of single crystals (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 216-221 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The components of a symmetric second-rank tensor (e.g. the strain tensor) can be calculated from measurements of that tensor property in at least six directions. A system of simultaneous equations (t(m) = Σ6i = 1 amiti) must be solved. The coefficient matrix ami is determined by the measurement directions, and therefore it is of great importance to choose these directions properly. Part 1 deals with the necessary condition: rank (ami)〈〉 0. Rules are given by which it is easy to decide whether rank (ami) = 0 or rank (ami) ≷0 without calculating the rank. In part 2 methods are developed to find optimized sets of measurement directions. An optimized set is one for which the inevitable measurement errors will give errors of the calculated tensor components as small as possible. Special attention is given to the case of X-ray strain measurement of single crystals.
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  • 152
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    Average Rayleigh-wave velocity of a computer-simulated crystallographic plane (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 181-187 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A model is proposed for calculating the Rayleigh-wave velocity as obtained by an acoustic lens, taking into account the anisotropy of the material under study and the profile of the miniature acoustic probe. The results obtained by this model on different `cuts' of single-crystal silicon agree with both those published in the literature and our own experimental results. In addition, the model has been applied to the non-destructive thickness measurement of opaque thin films deposited on different anisotropic substrates. More significantly, using the model and experimental acoustic material signature (AMS) curves obtained with this acoustic measurement system, the thickness of tungsten thin films deposited on silicon (100) have been measured. The results are in good agreement with measurements made using a Rutherford back-scattering technique.
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    Report on a round-robin study of diffuse X-ray scattering (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 188-194 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The diffuse scattering in a volume in reciprocal space from NbC0.72 was measured on an absolute scale at two synchrotron sources (in the US and in Japan) and with a high-intensity rotating-anode source (in Japan). The shape and actual absolute intensities agreed to a few percent. Special problems associated with such measurements at a synchrotron are noted, especially with an insertion device. The high resolution possible at such sources reduces the need for an evacuated sample chamber. Detailed measurements can be completed in 1–2 d, making such studies much more accessible than is possible with sealed-tube X-ray generation.
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  • 154
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    Diffraction from quasi-crystals and disordered twinned aggregates (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 308-314 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Following the discovery of systems with diffraction patterns exhibiting icosahedral symmetry by Shechtman, Blecht, Gratias & Cahn [Phys. Rev. Lett. (1984), 53, 1951–1953], which is forbidden in classical crystallography, interest has centred on Penrose tiling and its generalizations as a model for the explanation of these patterns, although Pauling [Nature (London) (1985), 317, 512–514; Phys. Rev. Lett. (1987), 58, 365–368] has proposed an alternative explanation in terms of crystal twinning. In an attempt to reconcile these two points of view a computer algorithm has been developed, following the methods outlined by Wolny, Pytlik & Lebech [J. Phys. C (1988), 21, 2267–2277], to grow a number of different structures which all tile the two-dimensional (2D) plane without defects. With the same two types of basic unit, it is shown that it is possible, on the one hand, to produce structures similar to the Penrose tiling pattern and, on the other, different types of twinned and disordered structures, with a continuous sequence of intermediates. Optical diffraction patterns of these structures have been obtained for comparison with real quasi-crystals.
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    High-pressure single-crystal X-ray diffraction studies of MoO3. I. Lattice parameters up to 7.4 GPa. Erratum (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 380-380 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Owing to a printer's error, the fourth equation given in the Abstract of the paper by Åsbrink, Kihlborg & Malinowski [J. Appl. Cryst. (1988). 21, 960–962] is incorrect. The correct equation is {\bar \beta}_c(0–7.41 GPa) = −3.35 × 10−4 (GPa)−1.
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  • 156
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    NRCVAX – an interactive program system for structure analysis (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 384-387 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: NRCVAX is a complete system of programs, covering all aspects of crystal structure analysis from data reduction to the presentation of results. The system, which is written in a `neutral' Fortran 77, presently exists in two forms. The first runs on a VAX computer under VMS, on an 80386 PC under UNIX and under IBM VM/CMS and MVS/TSO. The second is an adaptation which runs on PC-XT, AT, PS/2 and comparable microcomputers under MS-DOS. The two versions differ somewhat in structure, but very little in code, operation or functionality except for the graphics. The many options of the programs can be selected in a highly interactive manner and because of this the system is very flexible. Most options are assigned default values, however, and it is usually safe to run the routines with a minimum of user input using the defaults. The system will accept data from a wide variety of sources and has interface routines for several other systems. Graphics in the VAX/UNIX version are based on the widely available Tektronix 4000 series protocol, while the microcomputer version supports most common display adapters. It is also possible to prepare files for a variety of plotters, dot-matrix printers and laser printers. Source code is distributed and it should not be difficult to adapt the system to any computer with virtual memory and a Fortran 77 compiler.
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    A procedure for the selection and transferring of crystals at low temperatures to diffractometers (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 394-395 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    DREADD – data reduction and error analysis for single-crystal diffractometer data (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 396-397 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    New Commercial Products (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 398-400 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    Crystal data for p-bromochlorobenzene/p-dibromobenzene mixed crystals at 293 K (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 202-202 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The powder data for p-bromochlorobenzene/p-dibromobenzene mixed crystals [pBCB]x[pDBB]1 − x at 293 K are reported; their thermal stability at 293 K is given. Vertical diffractometer, graphite monochromator, Cu Kα, λ = 1.54056 Å. They are all isomorphous, monoclinic, P21/a with Z = 2. a = 15.176(6), b = 5.847(3), c = 4.078(2) Å, β = 112.57(3)°, V = 334.2 Å3, Dx = 1.947 Mg m−3 for [pBCB]0.90[pDBB]0.10; JCPDS No. 36-1975. a = 15.222 (7), b = 5.847 (3), c = 4.083(2) Å, β = 112.60(3)°, V = 335.5 Å3, Dx = 1.984 Mg m−3 for [pBCB]0.80[pDBB]0.20; JCPDS No. 36-1974. a = 15.260(5), b = 5.839(2), c = 4.084(2) Å, β = 112.57(1)°, V = 336.1 Å3, Dx = 2.024 Mg m−3 for [pBCB]0.70[pDBB]0.30; JCPDS No. 36-1973. a = 15.298(4), b = 5.845(3), c = 4.091(2) Å, β = 112.60(2), V = 337.7 Å3, Dx = 2.058 Mg m−3 for [pBCB]0.60[pDBB]0.40; JCPDS No. 36-1972. a = 15.340(4), b = 5.844(2), c = 4.092(2) Å, β = 112.60(2)°, V = 338.7 Å3, Dx = 2.096 Mg m−3 for [pBCB]0.50[pDBB]0.50; JCPDS No. 36-1971. a = 15.370(5), b = 5.843(2), c = 4.097(2) Å, β = 112.62(2)°, V = 339.6 Å3, Dx = 2.134 Mg m−3 for [pBCB]0.40[pDBB]0.60; JCPDS No. 36-1970. a = 15.404(6), b = 5.840(2), c = 4.100(2) Å, β = 112.67(2)°, V = 340.4 Å3, Dx = 2.172 Mg m−3 for [pBCB]0.30[pDBB]0.70; JCPDS No. 36-1969. a = 15.437(5), b = 5.842(2), c = 4.103(2) Å, β = 112.66(2)°, V = 341.4 Å3, Dx = 2.209 Mg m−3 for [pBCB]0.20[pDBB]0.80; JCPDS No. 36-1968. a = 15.468(4), b = 5.838(2), c = 4.104(2) Å, β = 112.70(2)°, V = 341.9 Å3, Dx = 2.249 Mg m−3 for [pBCB]0.10[pDBB]0.90; JCPDS No. 36-1967.
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    The energy dependence of the neutron coherent scattering length of europium (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 476-482 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: General considerations are given for the importance of providing an energy/wavelength-dependent database of neutron coherent scattering lengths, and of the possibility of constructing such a base from the range of neutron cross-section data that are generally available for a wide range of nuclides. The case of europium is considered in detail, partly because it is a good example of an element with strong resonance effects in the wavelength region of importance in crystallographic and condensed-matter studies, and partly because it is an exceptional case from the nuclear point of view, having multi-level interference effects. From the available cross-section data the complex coherent scattering length is constructed as a function of neutron energy up to 0.7 eV, for the isotopes and for the natural element. Some single-level approximations for the scattering-length function of 151Eu are given.
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    Correction for detector misalignment in a four-circle diffractometer (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 222-223 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The treatment of the angular errors arising in a four-circle diffractometer from the displacement of the detector slit and collimator from the equatorial plane is described. The method affords an accurate means of assessing and correcting the displacement from measured setting angles.
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    Collection and processing of X-ray diffraction data from protein crystals at high pressure (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 208-213 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Apparatus for collecting X-ray diffraction data from protein crystals at pressures up to 0.2 GPa is described. The modified techniques required for crystal mounting, determination of crystal orientation in the beryllium pressure cell, and centering in the X-ray beam are described. Special attention is required for intensity absorption corrections due to the marked attenuation (90%) of the beam. Data have been collected from tetragonal hen egg white lysozyme crystals at 1000 atm to 2.0 Å nominal resolution using Cu Kα radiation (1 atm = 1.01325 × 105 Pa). The crystals, crystallized in 0.86 M NaCl, require 1.4 M NaCl in the stabilizing solution to prevent cracking at several hundred atmospheres and higher. The crystals show no measurable hysteresis when cycled through several 1 to 1000 atm transitions. Altered intensities relaxed to their new value within 1 min on pressurization, but required about 90 rain to recover their starting values on pressure release. The unit-cell volume decreases 1.1% at 1000 atm.
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    A Monte Carlo error simulation applied to calibration-free X-ray diffraction phase analysis (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 217-221 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Quantitative phase analysis of a system of n phases can be effected without the need for calibration standards provided at least n different mixtures of these phases are available. A series of linear equations relating diffracted X-ray intensities, weight fractions and quantitation factors coupled with mass balance relationships can be solved for the unknown weight fractions and factors. Uncertainties associated with the measured X-ray intensities, owing to counting of random X-ray quanta, are used to estimate the errors in the calculated parameters utilizing a Monte Carlo simulation. The Monte Carlo approach can be generalized and applied to any quantitative X-ray diffraction phase analysis method. Two examples utilizing mixtures of CaCO3, Fe2O3 and CaF2 with an α-SiO2 (quartz) internal standard illustrate the quantitative method and corresponding error analysis. One example is well conditioned; the other is poorly conditioned and, therefore, very sensitive to errors in the measured intensities.
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    Quantitative texture measurement on thin wires (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 533-538 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A method is proposed for measuring textures on the surfaces of thin wires. The method is based on a numerical absorption correction analysis of the sample. Analytical formulas are given for thicker or more strongly absorbing specimens. Experimental work is presented to illustrate the use of the method.
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    Grazing-incidence small-angle X-ray scattering: new tool for studying thin film growth (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 528-532 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Grazing-incidence small-angle X-ray scattering (GISAXS) is introduced as a method of studying discontinuous thin films. In this method, the incident beam is totally externally reflected from the substrate followed by small-angle scattering of the refracted beam by the thin film. The experiment described establishes the ability of GISAXS to provide size information for islands formed in the initial stages of thin film growth. The data presented are for gold films of 7 and 15 Å average thicknesses on Corning 7059 glass substrates. The advantages of this technique are that it is non-destructive, can be done in situ, provides excellent sampling statistics, does not necessarily require a synchrotron source, and is not limited to thin or conducting substrates.
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    Calculation of the crystal orientation distribution function from synchrotron radiation experimental data (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 559-561 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Series-expansion coefficients for an orientation distribution function (ODF) of cold-rolled aluminium sheet were calculated from the intensity of Debye–Scherrer rings obtained in an experiment using synchrotron radiation. Calculated and observed pole figures demonstrate that a sufficiently good approximation to the ODF is obtained from coefficients calculated to l = 8.
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    X-ray study of CuGaxIn1−xSe2 solid solutions (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 578-583 
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    Notes: The semiconducting compound CuGaxIn1 − xSe2 crystallizes in the chalcopyrite structure (space group I{\bar 4}2d, Z = 4). The X-ray powder data for x = 1, 0.75, 0.6, 0.5, 0.4, 0.25 and 0.0 have been collected and it is found that the lattice parameters a and c and their ratio c/a vary linearly with x. Thus the composition of any chalcopyrite in the pseudo-binary system CuGaSe2 and CuInSe2 can be obtained from the accurate lattice parameters. The crystallite size determined from the (112) plane is minimum for x = 0.50 ( ̃1000 Å) and away from x = 0.50 it increases. A value of u = 0.240 (5) has been established for fixing the Se-atom positions in the CuGa0.5In0.5Se2 solid solution. The JCPDS Diffraction File No. for CuInSe2 is 40-1487 and for CuGa0.5In0.5Se2 is 40-1488.
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    Crystallographers (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 641-641 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    J. D. Hanawalt Powder Diffraction Award (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 642-642 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    K-edge anomalous scattering in rubidium hydrogen tartrate (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 18-20 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Anomalous X-ray scattering terms for Rb+ near the K-edge measured in diffraction experiments with synchrotron radiation range up to 4.71 (6) for f′′ and down to −9.80 (11) for f′, in agreement with values derived from the absorption spectrum.
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    X-ray reflectivity of bent perfect crystals in Bragg and Laue geometry (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 35-42 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The X-ray reflectivity of bent perfect crystals is calculated from a model where the crystal is approximated by a stack of perfect-crystal lamellae which have a gradually changing orientation. A computer program is developed for calculation of the reflectivity of the composite crystal from the dynamical theory of diffraction. An approximate solution is also given where an analytical formula for the reflectivity of a non-absorbing lamella is used and the effects of absorption are calculated separately. Typically, in the Bragg case, the reflectivity curve has a steep edge and an exponentially falling slope, while in the Laue case the curve is almost rectangular if the absorption is not too large. The width of the curve is inversely proportional to the bending radius in both cases. Reflectivity curves were measured for the 111 and 400 reflections of Si with Mo Kα1 radiation. The agreement with analytical and computer calculations is good, particularly at small bending radii where the kinematical limit is approached.
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    A fast high-accuracy lattice-parameter comparator (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 63-69 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A method of measuring differences in lattice spacing with an accuracy of 1 part in 108 in a period as short as two minutes is described. The method uses one source of copper radiation and a triple-axis arrangement. Two of these axes are double-leaf silicon springs in monolithic crystal assemblies which achieve the high stability required by such measurements. Samples are easily changed and sequences of measurements are performed entirely under computer control. The method is demonstrated by a comparison of the lattice spacings of four samples which reveals differences of up to 60 parts in 108 between silicon crystals of different origins.
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    Radiographic test of sample arrangement in synchrotron radiation (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 77-78 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    An elastically bent silicon crystal as a monochromator for thermal neutrons (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 105-110 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Some experimental results are presented for an elastically bent perfect silicon crystal in a strongly asymmetric diffraction geometry as a neutron monochromator. The use of this unconventional geometry of the monochromator appears to be suitable for a wide (several centimetres) incident polychromatic beam, when, thanks to the spatial condensation of the diffracted neutrons (Fankuchen effect), a high monochromatic beam density may be obtained. Furthermore, when using focusing in real and in momentum space by adjusting an optimum bending radius, the intensity diffracted by a sample may be comparable even with the best mosaic monochromators such as highly oriented pyrolytic graphite (PG). A comparison is demonstrated on the rocking curves of a strongly mosaic Ni–Al(020) crystal obtained with the monochromatic beam from bent Si(111), Si(400) and from PG(002), Cu(220) mosaic monochromators.
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    Easy derivation of the formula relating the fluctuations of a binary system to the X-ray scattering intensity extrapolated to s = 0 (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 134-135 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Bhatia & Thornton [Phys. Rev. B. (1970), 2, 3004–3012] have derived the formula that relates the scattering intensity of a binary system to the Fourier transform of the local number density and concentration. For the intensity at the limit of zero scattering angle, the same formula can be derived by a much simpler process.
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    SGROUP – a program for determination of possible space groups from structure-factor listings (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 142-143 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    New Commercial Products (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 144-146 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    Laue film integration and deconvolution of spatially overlapping reflections (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 169-174 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Single-crystal synchrotron-radiation Laue photographs of protein crystals and viruses are densely populated and a considerable amount of spatial overlapping of spots often occurs on the films. An integration procedure which enables the efficient deconvolution of these spots in order to obtain their integrated intensity has been developed and implemented. Some results are given for glycogen phosphorylase b and tomato bushy stunt virus. A comparative study of reflections overlapped on one exposure and separated on another, taken from the same crystal at a longer crystal-to-film distance, gives merging statistics comparable to those from the treatment of spatially separated spots only. In all cases the majority of the spatially overlapped data is made available for subsequent analyses.
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    Absolute polarity of α-lithium iodate (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 211-212 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Previous reports by Rosenzweig & Morosin [Acta Cryst. (1966). 20, 758–761], Liminga & Abrahams [J. Appl. Cryst. (1976). 9, 42–47] and Svensson, Albertsson, Liminga, Kvick & Abrahams [J. Chem. Phys. (1983). 78, 7343–7352], that the more steeply pointed ends of α-LiIO3 crystals grown from aqueous solution with 3 ≤ pH ≤ 7 have the apex of each pyramidal IO−3 ion pointing toward the direction which develops a positive polarity (d33 〉 0) under tensile stress applied along the polar hexagonal axis, have been confirmed contrary to the conclusion of Yang Hua-guang, Zhang Dao-fan, Chen Wan-chun & Li Yin-yuan [J. Appl. Cryst.(1989). 22, 144–149]. The error leading to the latter conclusion is identified.
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    Crystallographers (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 223-223 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    EDAUTOCAL – a program to calibrate EDXRD detector systems (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 222-223 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Extreme asymmetric X-ray Bragg reflection of semiconductor heterostructures near the edge of total external reflection (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 228-233 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Synchrotron radiation has been used to measure the rocking curves from a (GaIn)(AsP) single layer grown on an InP (100)-oriented substrate. For angles of incidence ΦB = (ΘB − φ) ≤ 0.7° measured at the Bragg angle ΘB (φ is the angle between the diffracting lattice plane and the surface), the rocking curve (RC) is very strongly influenced by total external reflection (TER). This causes a decrease in the full width at half-maximum (FWHM) and an asymmetrical shape for the RC for small ΦB. Both of these effects are due to the Bragg-angle shift from the actual incident angle Φ which is not considered in the conventional dynamical theory. In this paper the essential influence of TER on any thin-layer rocking curve is investigated using a numerical solution of the extended dynamical theory. The pattern can be interpreted up to ΦB ≥ ΘC (ΘC is the angle of TER) by semiempirical incorporation of the results of the extended theory with the coupling formalism of Barrels, Hornstra & Lobeek [Acta Cryst. (1986). A42, 539–545].
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    Study of ferroelastic domains in HTMA crystals at the ferroelectric–ferroelastic transition (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 277-281 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The ferroelectric ferroelastic phase transitions of tetramethylammonium tetrachlorozincate (HTMA) were observed by standard X-ray topography and by synchrotron topography. Observation of the phase boundary is possible in the latter case. The different kinds of domain walls observed in the ferroelastic phase cast doubts on the commonly assumed symmetry group of this phase.
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    Convolutional approach to the normalization of intensity scattered by polycrystalline substances (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 180-185 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A theory is presented describing convolutional properties of the reduced intensity distribution (intensity divided by the square of the atomic factor and multiplied by the scattering-vector length). The approximation used, verified on model data, leads to a relation between the effect of the multiple running average routine applied to reduced intensity and both normalization constant and local atomic density in the neighbourhood of any given atom. This enables an estimate of the normalization constant and the local density to be made with a high degree of accuracy. The effect of the choice of adjustable parameters in the running average routine is discussed. The procedure to calculate the interference function in the presence of an unknown background varying slowly with the scattering vector is presented.
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    An omega-scan artifact observed in Nicolet P3F diffractometers (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 212-214 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: This paper describes an instrumental artifact which has been observed in three Nicolet P3F diffractometers. In cases where the peaks are very sharp in ω, the artifact causes azimuthal or ψ scans to appear very noisy and to show a complex periodic variation of intensity with ψ. These intensity variations are reproducible. A simple correction is described which, when applied to the data, dramatically improves the appearance of these aberrant ψ scans. This correction is not limited to ψ scans and should improve the quality of all data collected on the machine.
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    A procedure for the generation of the symmetry of the multiple implication function from the crystal symmetry (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 225-227 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A computer-oriented procedure for the generation of the symmetry of the multiple implication function has been developed. The symmetry of the multiple implication function, referred to its own conventional unit cell, is tabulated for all space groups.
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    Auto-indexing of oscillation images (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 253-257 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A method is presented which indexes spots recorded on single oscillation images without any a priori knowledge of cell parameters. The strategy is similar to that used in four-circle diffractometry and the method works in a fully automatic manner. It is applicable to multiple oscillation images or multiple stills. A complementary method is also described to obtain orientation angles for the case where cell parameters have already been determined.
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    A high-resolution Weissenberg camera for X-ray synchrotron radiation (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 351-354 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A photographic Weissenberg camera has been constructed which can be mounted on the 2θ arm of a four-circle diffractometer. At a distance of 0.5 m from the sample the 2θ resolution for a 100 μm crystal is 0.2 mrad (0.01°), allowing a high-resolution mapping of reciprocal space at a synchrotron source in an efficient way. As sample experimental results, a study is presented of the streak system around the 111 reflection of a perfect germanium crystal and the detection of a minute phase transformation in a single-powder grain of a high-Tc superconductor.
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    Improvements to the Chebyshev expansion of attenuation correction factors for cylindrical samples (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 378-386 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The accuracy of the Chebyshev expansion coefficients used for the calculation of attenuation correction factors for cylindrical samples has been improved. An increased order of expansion allows the method to be useful over a greater range of attenuation. It is shown that many of these coefficients are exactly zero, others are rational numbers, and others are rational fractions of π−1 The assumptions of Sears [J. Appl. Cryst. (1984), 17, 226–230] in his asymptotic expression of the attenuation correction factor are also examined.
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    High-pressure single-crystal study on AlPO4 with synchrotron radiation (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 397-400 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A single-crystal study on AlPO4 was performed at 2.90 (7) GPa with synchrotron radiation using a diamond-anvil cell with a beryllium gasket. For the data collection the radiation wavelength of only 0.54 Å, was chosen to minimize the absorption of X-rays in the pressure cell. The diffracted intensity was high enough to measure even weak reflections with sufficient counting statistics. The refined structural parameters are in good agreement with those determined from data collected with a conventional X-ray tube.
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    Structural study of Cd(S,Se) doped glasses. High-resolution transmission electron microscopy (HRTEM) assisted by image processing (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 418-423 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: High-resolution transmission electron microscopy (HRTEM) was used for examining Cd(S,Se) nanocrystals grown in silicate glasses commercially available as optical filters. The lattice images of the nanocrystals were numerated and submitted to filtering through Fourier transformation in order to sweep off the background signal originating mainly from glass. Optical filters from several firms were examined. The nanocrystals have been identified with Cd(S,Se) compounds crystallized in the wurzite structure, as in bulk material. The lattice images indicate crystallites having the shape of hexagonal prisms a little elongated along the c axis. The distribution of grain size differs according to the filter: the smallest size being about 1.5 nm (threshold for detection), the largest size varies from 7 to 10 nm, the average size sa, from 3–4 to 5–6 nm and the characteristic size sc from 5–6 to 7–8 nm (sc is the size of grains occupying the main part of the crystallized volume).
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    Silicon photodiode detector for small-angle X-ray scattering (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 430-432 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A photodiode X-ray detector was built to measure small-angle X-ray scattering (SAXS) at a synchrotron-radiation source in conjunction with a double-crystal diffractometer SAXS camera at photon energies between 5 and 11 keV. The photodiode detector response in this energy range is linear at photon counting rates up to 1012 photons s−1 and thus it was not necessary to attenuate the monochromatic X-ray beam with calibrated foils. SAXS data taken with a scintillation counter and the photodiode detector are compared, demonstrating marked improvement in counting statistics, rate of data acquisition and signal-to-noise ratio.
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    Sub-nanosecond X-ray powder diffraction (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 441-443 
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    Notes: The X-rays emitted from a laser-produced plasma have been used to obtain powder diffraction patterns with exposures of less than a nanosecond. The X-rays were produced by focusing approximately 50 J of 0.53 μm laser light in a 600 ps (FWHM) pulse to a tight (1̃00 μm diameter) spot on a solid titanium target. The spectral brightness of the resonance line of the helium-like titanium thus produced was sufficient to record diffraction from LiF powder in a single exposure using the Seemann–Bohlin geometry. These results indicate that time-resolved measurements of the lattice parameters of polycrystalline materials can be made with sub-nanosecond temporal resolution.
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    New Commercial Products (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 446-446 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    A position-sensitive detector system for the measurement of diffuse X-ray scattering (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 476-484 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The use of a one-dimensional position-sensitive detector for diffuse X-ray scattering measurements is described. Calibration procedures for scattering angle and intensity measurements are discussed. Some nonuniformities have been found in the counting efficiency as a function of distance along the detector. A procedure is described for measuring the diffuse scattering in a section of reciprocal space.
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    Short-range-order determination in quenched NbC0.73 by elastic diffuse neutron scattering (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 497-508 
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    Notes: The elastic diffuse neutron scattering of an NbC0.73 single-crystal has been measured at room temperature on two different spectrometers, the four-circle D10 at the HFR–ILL (Grenoble), and the two-axis G44 with time-of-flight analysis at the Laboratoire Léon Brillouin (Saclay). The data were treated either by Fourier transformations or by least-squares fit. The short-range-order parameters and the interatomic static displacements obtained by the various experiments and/or data treatment are in good agreement: carbon vacancies tend to be third neighbours in the f.c.c. metalloid sublattice and metal atoms relax away from the vacancy first neighbours by 0̃.05 Å. It is shown that the treatment of diffuse scattering data limited to two reciprocal planes [(001) and (1{\bar 1}0)] gives satisfactory results.
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    Electron-density distribution from X-ray powder data by use of profile fits and the maximum-entropy method (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 526-534 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Following the profile decomposition of CeO2 X-ray powder data into individual structure factors, the maximum-entropy method (MEM) has been used to obtain an electron-density-distribution map. In the profile decomposition process, it is impossible to avoid the problems of overlapping peaks which have the same magnitude of reciprocal vectors, such as d*(511) and d*(333), for a cubic crystal, or very severely overlapping reflections. The formalism to treat such overlapping reflections in the MEM analysis is to introduce combined structure factors. The maximum value of the scattering vector, 4π(sinθ)/λ, which was used in the present analysis is small (about 7.8 Å−1) but the resulting electron-density-distribution map is of a high quality and much superior to the conventional map. As a consequence, the ionic charge of Ce and O ions can be obtained with reasonable accuracy from the MEM density map. Furthermore, the map reveals the existence of electrons around the supposedly vacant site surrounded by eight O atoms, which is probably related to the high ionic conductivity of this substance.
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    SYMABS – an interactive program for checking systematic absences caused by lattice centering, glide planes and screw axes (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 558-558 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Prices of Acta Crystallographica and Journal of Applied Crystallography (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 560-560 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889890009827
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