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  • National Academy of Sciences  (12,418)
  • International Union of Crystallography (IUCr)
  • American Physical Society (APS)
  • 1990-1994  (19,581)
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Publisher
Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    Multiple scattering of X-rays in the case of isotropic samples (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 11-17 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The contribution of multiple scattering in wide-angle X-ray scattering experiments on isotropic samples using Mo Kα and Cu Kα radiation is estimated. The portion of doubly and triply scattered intensity was calculated with a tedious Monte Carlo simulation method and the portion of doubly scattered intensity was calculated with a fast approximate numerical integration procedure. In the case of light elements the correction was found to be important. The approximate method proved to be reliable for thin samples in cases where the cross section for inelastic scattering is small. The effect of the molecular structure of the material on the multiply scattered intensity was demonstrated in the case of liquid sulfur and found to be meaningful at small scattering angles. The correction method was applied to the radial atomic density function (RDF) analysis of water and sulfur. The correction improved the behaviour of the reduced interference function but its effect on the RDF was small in both cases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889889009283
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  • 2
    Electronic Resource
    Electronic Resource
    Transmission electron microscope studies of phase transitions in single crystals and ceramics of ferroelectric Pb(Sc1/2Ta1/2)O3 (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 43-54 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An account is given of transmission electron microscope investigations of the phase transitions in single crystals and ceramics of the complex perovskite structured ferroelectric `relaxor' compound Pb(Sc1/2Ta1/2)O3. The crystal symmetries pertaining to both the non-polar paraelectric (PE) and polar ferroelectric (FE) states have been studied by the technique of convergent-beam electron diffraction. A new phase transition has been discovered in the temperature range for which the FE and PE states coexist. The new phase transition is interpreted as the creation of a modulated antiferroelectric state, and this is viewed as marking a departure from relaxor behaviour towards more `normal' ferroelectric behaviour.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S002188988901085X
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  • 3
    Electronic Resource
    Electronic Resource
    High-resolution electron microscopic study on long-period superstructures with 6H stacking sequence in Au3Cd alloys (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 55-62 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Atomic arrangements of long-period superstructures in Au–24.5at.%Cd alloy with the basic h.c.p. structure have been investigated by high-resolution electron microscopy. The alloy shows one-dimensional or two-dimensional long-period superstructures in the close-packed plane with a 6H stacking sequence, depending on heat treatments. It is shown that the two-dimensional incommensurate superstructure with a period larger than 9a0 is composed of domains of the hexagonal commensurate structure (M = 9) separated by the antiphase-boundary zone in which 33/2a0 × 2a0 × 3c0 orthorhombic structure is formed (a0, c0 being the lattice parameters of the h.c.p. structure). Microstructures of the alloy annealed at 620 K with the one-dimensional long-period superstructure and of the alloy quenched from 770 K showing diffuse scattering have also been investigated by high-resolution electron microscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889889011441
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  • 4
    Electronic Resource
    Electronic Resource
    Closed-form expressions for Fourier–Bessel transform of Slater-type functions (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 71-73 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Integrals of the type G_{N.k}(S,Z) = \int^{\infty}_{0}r^N{\rm exp}(- Zr)j_k(Sr){\rm d}r for k ≤ N − 1 have been directly evaluated and the closed-form expressions are given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889889010484
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  • 5
    Electronic Resource
    Electronic Resource
    The properties of anisotropic small-angle scattering (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 79-81 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: It is shown that the cross section of small-angle neutron scattering (SANS) on an anisotropic system of point scatterers is determined by a symmetric tensor (R). The mean square radius of gyration of the system is the trace of R. A simple method is proposed for experimental determination of the tensor R by small-angle measurements with rotation of a sample.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889889008253
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  • 6
    Electronic Resource
    Electronic Resource
    Linear least-squares adjustment of UB matrix elements and the prediction of reflection positions (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 111-114 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A method is presented for the linear least-squares refinement of small changes in the UB matrix elements and diffractometer offsets in single-crystal diffractometer experiments. It thus affords a rapid method for calculating the consequent changes in the positions of the centres of Bragg reflections.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889889013026
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  • 7
    Electronic Resource
    Electronic Resource
    Time modulation of small-angle neutron scattering in the longitudinally vibrating double-crystal system (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 70-71 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The use of two longitudinally vibrating perfect crystals is suggested for small-angle neutron scattering experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889889010241
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  • 8
    Electronic Resource
    Electronic Resource
    A versatile new cryostat for obtaining X-ray diffuse intensity data from thin flat single crystals (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 77-77 
    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/S0021889889011118
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  • 9
    Electronic Resource
    Electronic Resource
    Approximation of pole figures for the determination of crystal orientation in polymeric solids (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 88-93 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The approximation of experimentally measured angular intensity distributions of X-rays diffracted by oriented polycrystalline specimens is suggested as a method for the determination of orientation distribution characteristics for uniaxially oriented polymeric fibres. A non-linear optimization program based on a Hook–Jeeves algorithm is elaborated and incorporated into the method. As an example, the interpretation of the data from polyethylene specimens having various degrees of orientation is given. An important application of the method is the analysis of distributions (pole figures) using a superposition of two identical or similar functions with different parameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889889012185
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  • 10
    Electronic Resource
    Electronic Resource
    A HREM study of nonbasal twinning and superlattices in ilmenite (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 82-87 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The microstructures of natural ilmenite found in Panzhihua district, China, were examined by high-resolution electron microscopy (HREM). The [{\bar 1}2{\bar 1}0] structural images showed clearly the (10{\bar 1}1) nonbasal twinning which seems to be coincident with the [{\bar 1}012] rotation twinning. The superlattices with periodicities of 16.8 and 12.6 Å, respectively, as well as the unit-cell twinning related to the ordering of (10{\bar 1}1) multiple twinnings were observed. The superlattice resulting from the ordering arrangement of (10{\bar 1}1) stacking faults related to the slip systems suggested by Heuer [Philos, Mag. (1966), 13, 379–893] were also detected. Possible genetic aspects are considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S002188988901099X
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  • 11
    Electronic Resource
    Electronic Resource
    An evaluation of selected density-modification methods for protein-structure determination (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 115-131 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The effectiveness of density-modification methods in reducing phase errors has been quantitatively analyzed under conditions in which the source and magnitude of phase error could be defined. Progress was gauged by monitoring both the phase errors and electron density. Changes in electron density were monitored in and around the protein density and in the solvent density. The results of this analysis suggest that the improvement possible is more dependent upon the magnitude than on the source of phase error, and that the methods are most effective when the initial phase error is relatively small. As the magnitude of error increases, the improvement gained decreases, and in some cases noise is introduced by the procedure(s).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889889013233
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  • 12
    Electronic Resource
    Electronic Resource
    FIT, a computer program for decomposition of powder diffraction patterns and profile analysis of pair correlation functions (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 138-140 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: FIT is an interactive computer program for fitting analytical models to powder diffraction patterns and to pair correlation functions. FIT has been written in Turbo C and runs on IBM XT/AT or compatible personal computers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S002188988901410X
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  • 13
    Electronic Resource
    Electronic Resource
    PLOTQ – a computer program for displaying electron densities and related functions in two and three dimensions (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 143-144 
    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/S0021889889011738
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  • 14
    Electronic Resource
    Electronic Resource
    Auto-indexing of oscillation images (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 253-257 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889890002461
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  • 15
    Electronic Resource
    Electronic Resource
    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 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889890002709
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  • 16
    Electronic Resource
    Electronic Resource
    An automated system for micro-batch protein crystallization and screening (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 297-302 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An automatic sample dispenser has been constructed to aid with protein crystallization trials. This dispenser contains a bank of Hamilton syringes driven by stepper motors under computer control which is used to set up small samples (2 μl or less) for batch crystallization. Software has been written to create a series of trials which form a two-dimensional array of crystallization conditions. A specially designed fluoropolymer multibore microtip allows the very small volumes to be mixed and dispensed with great accuracy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889890003260
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  • 17
    Electronic Resource
    Electronic Resource
    Neutron topography as a tool for studying reactive organic crystals: a feasibility study (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 186-198 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The feasibility of using neutron topography as a non-destructive imaging technique for the study of X-ray sensitive organic single crystals, with a view to applying it to the study of reactivity in such crystals, has been tested. Crystals studied range from relatively X-ray insensitive protonated and deuterated pyrene crystals to relatively highly X-ray sensitive 2,4-hexadiynylene bis(p-toluenesulfonate) (PTS) monomer crystals. The latter crystals are readily polymerized in an X-ray beam. Results indicate that neutron topographic imaging provides little advantage over X-ray topography for either the X-ray insensitive or X-ray sensitive crystals studied here. It was concluded that this is mainly due to limitations in spatial resolution attributed to geometric effects inherent to the technique. However, for X-ray sensitive crystals, neutron topography can provide useful information, in a non-destructive way, in the form of rocking-curve data, and as such can be regarded as a useful `ally' technique to the analogous X-ray techniques. It is expected that in the case of extreme X-ray sensitivity, provided geometric losses can be minimized, neutron topography may be the only technique capable of non-destructively revealing bulk defect structures and strain distributions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889890000371
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  • 18
    Electronic Resource
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    Enhancement in resolution and lack of radiation damage in a rapidly frozen lysozyme crystal subjected to high-intensity synchrotron radiation (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 215-218 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: X-ray data have been collected from a monoclinic hen egg-white lysozyme (HEWL) crystal, rapidly frozen at 120 K on the end of a glass fiber, using high-intensity synchrotron X-radiation. A comparison of oscillation photographs taken at the beginning and end of data collection shows no evidence of radiation damage even though the crystal was exposed in the synchrotron beam for 8̃ h. Not only are the low-resolution data unaffected by radiation damage but the high-resolution data remain unaffected as well. There is also a marked improvement in the resolution of the diffraction pattern of the rapidly frozen crystal when compared to a similarly sized crystal irradiated in a capillary tube at room temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889890001893
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  • 19
    Electronic Resource
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    The physics of quasicrystals edited by P. J. Steinhardt and S. Ostlund (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 224-224 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889890001170
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  • 20
    Electronic Resource
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    Reduction of parasitic scattering in small-angle X-ray scattering by a three-pinhole collimating system (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 241-245 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A series of experiments have been undertaken on the Oak Ridge National Laboratory (ORNL) 10 m small-angle X-ray scattering (SAXS) camera to provide quantitative data on the level of background (parasitic) scattering generated by different types of bevelled collimating slits. The addition of a third (guard) slit, positioned close to the sample, resulted in a reduction of over an order of magnitude in the parasitic background generated by the best two-slit combination of collimating slits. This made it possible to reduce the size of the beamstop, permitting useful data to be collected down to a value of the scattering vector Q = 4πλ−1sinθ ∼ 3 × 10−3 Å−1, where λ is the wavelength, and 2θ is the angle of scatter. This permits the resolution of distances d ̃2π/Q up to 2000 Å.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889890001984
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  • 21
    Electronic Resource
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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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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889890005702
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  • 22
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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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    URL: http://dx.doi.org/10.1107/S0021889890006379
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  • 23
    Electronic Resource
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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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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889890005167
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  • 24
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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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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889890008500
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  • 25
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    A two-circle powder diffractometer for synchrotron radiation with a closed loop encoder feedback system (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 292-296 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A high-angular-resolution two-circle powder diffractometer equipped with long diffracted-beam collimators has been built at Daresbury Laboratory. The diffractometer has encoders mounted directly on the 2θ and ω axes. These give a nominal angular resolution of 0.1 and 1.0 mdeg respectively. Repeated scans of single powder peaks have demonstrated a reproducibility of 0.1 mdeg 2θ. Measurements on five independent peaks of tungsten give a self consistency of 1(1) × 10−5 Å. An example data set from synthetic olivine Mg2SiO4 has been refined using the Rietveld method and the results compare very well with single-crystal structure refinements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889890003648
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  • 26
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    Analytical treatment of the resolution function for small-angle scattering (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 321-333 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Analytical expression for the resolution function for small-angle scattering in pinhole geometry are derived. The contributions to the resolution function due to wavelength spread, finite collimation and detector resolution are determined separately using Gaussian functions to approximate the contributions. A general resolution function is derived which is the result of the combined effect of the three contributions. An azimuthal-integrated resolution function, which can be applied to scattering from a material with a circular symmetric scattering cross section, is calculated. This resolution function contains in addition a contribution from the averaging procedure itself. The analytical results are compared with the results of computer simulations. The comparison shows that Gaussian functions give a good description of the resolution function and that the widths agree with those calculated by the analytical expressions. The resolution function is applied in the analysis of two experimental examples: neutron scattering from latex particles [Wignall, Christen & Ramakrishnan (1988). J. Appl. Cryst. 21, 438–451] and neutron scattering from lamellar structures of bilayer lipid membranes (Mortensen, Pfeiffer, Sackmann & Knoll, unpublished). The analytical expressions for the resolution function allow a least-squares analysis to be performed and excellent agreement between experimental and theoretical scattering patterns are obtained.
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    URL: http://dx.doi.org/10.1107/S0021889890003946
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  • 27
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    A convenient translation-function parameterization (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 341-343 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A novel parameterization is given for one type of single-symmetry-element translation function, the Q functions of Tollin [Acta Cryst. (1966), 21, 613–614]. This parameterization enables the straightforward computation of these for any symmetry element. A computationally convenient form of the Q-function expression is given. Examples of Q for a selection of symmetry elements, illustrating some of the simplifications of the general form.
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    Crystallographers (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 349-350 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    URL: http://dx.doi.org/10.1107/S0021889890005726
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    X-ray diffuse scattering of a decomposing hexagonal alloy (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 458-461 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A new type of X-ray diffuse scattering has been found in the early stages of decomposition of the hexagonal phase of Mn–44at.% Al. The diffuse scattering is observed mainly within the basal plane of the reciprocal lattice and differs for the 10{\bar 1}l and 11{\bar 2}l points. Theoretical calculations of the X-ray diffuse scattering according to the kinematic scattering theory have been performed for the elastically isotropic and anisotropic cases and for precipitates of various forms and orientations with and without a depleted layer surrounding them. In the latter case, a zero-intensity region near the reciprocal-lattice points occurs. There are cases of good agreement between the experimental results and calculations for the precipitates with a depleted layer.
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    Array-type universal profile function for powder pattern fitting (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 485-491 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An array-type universal profile function for powder-pattern fitting is described. It is defined as an array of unknown parameters representing the profile heights at discrete angular steps. The unknown parameters are determined during least-squares fitting together with the integrated intensity, the peak position, the peak width and background parameters. The function has been applied to profile fitting in a small 20 range, and has better R-factors than the pseudo-Voigt and Pearson VII functions. This new function has some important advantages: it can model any complex profile shape, which would be difficult to describe by a smoothly varying analytical-type function; it generally gives a better fit and thus more precise and accurate analysis than currently used analytical-type functions; and it can be applied to the data of all radiation sources including conventional X-rays, synchrotron radiation and time-of-flight and fixed-wavelength neutrons without changing the mathematical form. The optimized use of the function and the accuracy of deduced parameters are also discussed.
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    Automatic evaluation of general spot profiles in oscillation photography (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 549-553 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An algorithm to determine the exact profiles of digitized spots having arbitrary shapes and sizes is described. It does not require any prior knowledge of crystallographic parameters and can be applied to the digitized data set of any random distribution of arbitrarily shaped peaks of finite size having an average intensity significantly higher than a nearly constant background. Application to the case of oscillation photography data from protein crystals is described.
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    Crystallographers (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 559-559 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    Absorption contrast effects in the quantitative XRD analysis of powders by full multiphase profile refinement (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 14-17 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: It is shown that quantitative X-ray powder diffraction analyses using full profile multiphase refinement should include corrections for the Brindley particle absorption contrast effect. This is demonstrated with synthetic mixtures of the highly contrasting phases LiF and Pb(NO3)2 (μ/ρ = 20 and 231 cm−1 for Co Kα). With contrast corrections, the only parameter which needs to be input is an effective particle radius R for each phase. For mixtures of LiF and Pb(NO3)2 over the whole composition range, quantification is achieved, under the present specimen preparation method, with an effective particle radius of 51 μm for both phases, giving analyses correct to within 1 percentage point. Without Brindley corrections, the analysis is grossly in error.
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    The application of synchrotron X-radiation for the study of phase transitions in lipid model membrane systems (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 48-60 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The use of real-time X-ray diffraction techniques to characterize phase transitions in lipid systems is reviewed. Information such as transition mechanism and thermodynamic order can be correlated with thermodynamic data from scanning calorimetry or densitometry to describe completely the measured thermodynamic quantities in terms of structural phenomena. Dynamic phase information can also be used to produce dynamic phase diagrams which define the parameters for creation of metastable phases in these systems. Examples involving changing lipid and solvent composition are provided to illustrate the utility of the approach.
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    Anomalous small-angle X-ray diffraction of an Nd-Fe multilayer (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 156-163 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The Bragg peak intensities, related to the electronic concentration profile, depend both on atomic concentrations and on specific volumes. Anomalous dispersion, using synchrotron radiation, produces a variation of the scattered intensity, which in principle allows a separation of the two contributions. The kinematic approximation for diffraction of thick multilayers allows an easy evaluation of the ratio of specific volumes, but the entire reflectivity curves and their deformations with photon wavelength can be explained by the interferences between the Kiessig fringes and diffraction maxima in a kinematic approximation. A full optical treatment confirms the previous analysis. Finally, the relaxations occurring during Nd–Fe interdiffusion are too small to be measured in our experimental conditions.
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    Structure determination of LiMoP2O7 from multiphase powder X-ray diffraction data (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 520-525 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The crystal structure of LiMoP2O7 was determined from conventional powder X-ray diffraction at room temperature in the presence of MoP2O7, MoO2 and Mo as impurities. Pattern decomposition was employed to eliminate complex contaminants prior to the Rietveld structure refinement. LiMoP2O7 crystallizes in the space group P21 with Z = 2, a = 4.8987 (3), b = 8.3912 (4), c = 7.0306 (4) Å, β = 109.327 (4)°, V = 272.71 Å3. Final agreement indicators were Rp = 0.0589, Rwp = 0.0772, RF = 0.054 and RI = 0.080. The framework of the structure consists of corner-sharing MoO6 octahedra and P2O7 groups, which form tunnels where the Li cations are located. The results give an example of analyzing a structure from a tetraphasic mixture using pattern decomposition in conjunction with the Rietveld refinement method.
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    XENVIEW - an interactive program to display and analyze electronic area detector data (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 196-196 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    URL: http://dx.doi.org/10.1107/S0021889890010676
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    A standardless method of quantitative mineral analysis using X-ray and chemical data (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 197-202 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A complex standardless mineral-analysis method is described which determines both the concentrations and the chemistry of minerals in a batch of m ≤ w + t suitable rock samples, where w and t are the numbers of crystalline and amorphous minerals, respectively. The method is based on data from X-ray diffractometry and the bulk chemistry of the samples. Analytical examples are given. The problem of the accuracy of the analysis is discussed.
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    The influence of laser radiation on X-ray diffraction in ferroelectric crystals with nonlinear optical properties (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 74-76 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The influence of laser radiation (λ = 532, 630 nm) on X-ray diffraction in nonlinear ferroelectric LiNbO3:Fe(0.01–0.02%) and triglycine sulfate (3C2H5NO2.H2O4S) crystals has been studied. The laser radiation was applied to the sample on a four-circle X-ray diffractometer through a flexible optical fiber. The end of the light guide was fixed in a special attachment installed on the goniometer head and allowed the laser beam to be oriented along some chosen direction in a crystal and to maintain this orientation during the whole process of data collection over the reflection sphere. The output power of laser radiation at the end of the light guide was 7 to 10 mW (or about 0.3 W cm−2). The sample irradiation by laser light led to a visible increase of intensity for some reflections (up to 34%). A noticeable difference in the extinction parameters of the samples was found between the sets of reflections measured under normal conditions and those measured under laser irradiation.
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    Effects of tetragonal distortion in thin expitaxic films on electron channeling patterns in scanning electron microscopy (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 102-107 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The elastic strain state in a 25 nm (In,Ga)As epitaxic film deposited on a (001) GaAs substrate includes a Poisson expansion perpendicular to the interface. This creates a tetragonally distorted lattice in the film which shifts high-order Laue-zone (HOLZ) lines in electron channeling patterns (ECP) from the film compared to ECP's from pure GaAs. The line shifts are predictable, thereby allowing measurement of elastic strains parallel and perpendicular to the film/ substrate interface independently. The technique appears to have an accuracy close to 0.2%.
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    Identification of planar defects by etch pits formed on the mantle surface of cylindrical single crystals (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 119-125 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The formation of etch pits directly on the mantle surface of cylindrical single crystals rather than on flat surfaces, as it is usually performed, allows easier and more accurate determination of the crystal orientation. The application of this technique to tungsten single crystals subjected to compression tests at low temperature allows an easy identification of the twinning systems. This technique is well adapted to single crystals subjected to mechanical tests mainly because it does not require the preparation of flat surfaces before or after the test to reveal etch pits. Producing flat surfaces could induce stress within the crystals that in turn could activate slip or twinning mechanisms and would, therefore, give wrong results.
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    Calculation of the refractive indices of molecular crystals (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 171-174 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The anisotropic optical properties of molecular crystals of general symmetry, which are characterized by three different refractive indices and corresponding optical axes, have been calculated by tensorial addition of the bond polarizabilities of all covalent bonds knowing the structure from X-ray diffraction analysis. As an example, refractive indices are given for β-phase fat crystals, viz glyceroltristearate and -tripalmitate, which are very hard to grow. Some of these refractive indices have been measured directly using the immersion method. Furthermore, average refractive indices of such crystals have been calculated by means of the Lorenz–Lorentz equation from the liquid data. As far as comparisons are possible, the theoretical values agree with experiments.
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    SEXIE - a microcomputer program for the calculation of coordination shells and geometries (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 263-263 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    Crystal engineering: the design of organic solids by G. R. Desiraju (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 265-265 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    Focusing double bent crystal (DBC) diffractometer for medium-resolution small-angle neutron scattering (SANS) experiments (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 298-303 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A new modification of a focusing SANS instrument where at least the first crystal is set for diffraction in the asymmetric transmission geometry is presented. Unlike an earlier version which employed both crystals in the symmetric Bragg-case geometry [Kulda & Mikula (1983). J. Appl. Cryst. 16, 498–504], the new modification permits one simultaneously to exploit the effects of natural wavelength focusing and space condensation of the diffracted beam due to asymmetric diffraction. This DBC instrument seems to be suitable for use with beams with a large cross section at the first crystal and for SANS experiments on samples with a small width (few mm).
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    High-symmetry triple junctions in polycrystalline silicon (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 232-238 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Triple junctions in polycrystalline silicon for solar cell applications have been studied by TEM (transmission electron microscopy). The typical characteristic of these junctions is the existence of high-symmetry interfaces, i.e. twins of different order. Whenever the triple junction contains two such interfaces, the intersection axis is a CSL (coincidence site lattice) symmetry axis. In this case the mutual relation of the grain boundaries of the triple junctions is revealed by symmetry rules, since the boundaries are described by symmetry elements of the corresponding CSL which do not belong to the symmetry group of the parent lattice. Therefore, the different variant orientations of these CSL symmetry elements, implied by the symmetry of the lattice, are used for the study of triple junctions. A junction is geometrically characterized by the point-group-symmetry properties. The observations concern symmetrically different triple junctions of the same type of macroscopically stable grain boundaries and faceted and microfaceted interfaces. It is shown that in silicon the thermodynamically favored twins are combined by specific symmetry rules. The results are discussed in accordance with the possible growth mechanisms.
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    Experimental verification of the triple isotopic substitution method in small-angle neutron scattering (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 243-254 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The theoretical predictions of the triple isotopic substitution (TIS) method in small-angle neutron scattering have been confirmed experimentally. A unique advantage of the method, namely the possibility to make part of a complex particle `invisible' in normal (H2O) buffer, is demonstrated. Particle association, the addition of `small' molecules (such as glycerol) or `large' molecules (such as pyruvate kinase) in the solutions under study have been shown not to influence the difference scattering curve obtained. The possibility of extracting normalized interparticle interference functions from the TIS data is discussed. This enables the detection of the presence of aggregates (e.g. dimers) in the solution, even in cases where the molar mass of a particle and/or its concentration are unknown. A simple internal test is suggested which checks whether or not sufficient conditions for the applicability of the method are fulfilled.
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    New Commercial Products (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 264-264 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    Experimental strategies in Laue crystallography (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 267-277 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The efficiency of data collection using the Laue technique varies with the wavelength range, the crystal symmetry, the orientation of the crystal in the X-ray beam, the crystal-to-film distance and the acceptance angle of the detector. By optimizing these parameters and by taking advantage of the diffraction symmetry represented by the Laue class, it is often possible to collect a nearly complete data set in one or two exposures. This paper discusses general strategies for data collection and presents results from a computer survey to find optimal crystal orientations for the eleven Laue classes.
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    SANS studies from porous alumina fibres (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 607-615 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The small-angle neutron-scattering pattern from bundles of 3 μm diameter porous alumina fibres has been determined and found to be anisometric. Intense scattering at a narrow divergent angle has been observed perpendicular to the fibre axes, coupled with a lower-intensity scattering over all other angles. The pattern has been analysed by means of sector analysis in order to determine the variation of intensity with modulus of the scattering vector over the range 0.006–0.2 Å−1. A theory has been developed to account for contributions to scattering from, firstly, macroscopic features of the fibres such as alignment distribution and lack of straightness and, secondly, from internal porosity allowing for distributions of size and of orientation with respect to the fibre axis. The parameters of the size distributions have been estimated from the two-dimensional data by directly fitting the scattering equations using a weighted non-negative least-squares principle.
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    Strain field due to a slip band near a grain boundary in an Fe-6at.% Si bicrystal. II. Interpretation of double-crystal topographs (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 324-330 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The lattice distortion due to the head of the slip band at the grain boundary is measured by double-crystal topography. The head of the slip band is approximated by a macrodislocation situated at the grain boundary. To interpret the topographs, the relaxation due to the free surface is included. The Burgers vectors of macrodislocations, i.e. the number of accumulated dislocations, are found.
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    Grazing-incidence X-ray scattering study of the microstructure of tungsten–carbon films (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 638-644 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The microstructure of a coating deposited onto a tungsten carbide layer by cathodic sputtering assisted by chemical vapour deposition (CVD) has been analysed by small-angle scattering of X-rays (SAXS) with a conventional laboratory set-up specially adapted for grazing incidence. Anomalous-scattering measurements have also been performed at LURE, the French synchrotron-radiation facility at Orsay with the aim of characterizing the structure of phases present in the coating. SAXS results reveal the existence of very small precipitates; the size of these precipitates determined from the use of the Guinier approximation is about 16 Å, the correlation length deduced from the position of the peak in the small-angle scattering pattern is about 36 Å. The value of the experimental integrated intensity and the variation of the observed intensities with photon energy lead to the conclusion that these nanocrystals are highly enriched in tungsten and embedded in a carbon-based matrix having a weak electronic density. Electron diffraction results support the assumption of the presence of β-WC1 − x, an unstable high-temperature phase. Furthermore, the low electronic density of the matrix is in agreement with face-centred-cubic carbon recently proposed in the literature.
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    Small-angle X-ray scattering study of lamellar microdomains in a block copolymer (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 679-684 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Lamellar microdomains formed in the solvent-cast films of a poly[styrene-block-(ethylene-alt-propylene)] (SEP) diblock polymer were studied by small-angle X-ray scattering (SAXS). The SAXS profiles, displaying a series of peculiar scattering maxima which cannot be ascribed to the higher-order diffraction maxima from a regular lamellar spacing, were analyzed based on a model of the one-dimensional paracrystal with a preferential orientation. The results suggest that these maxima are due to higher-order scattering maxima from single lamellar microdomains. The maxima suggest that the relative standard deviation for the distribution of the polystyrene lamellar size is much smaller than that of the lamellar spacing, giving rise to a situation in which the oscillation of the particle factor with scattering vector h persists up to high h values while that of the lattice factor damps to unity at low h values. The SAXS result was interpreted as being due to a bending distortion of the polystyrene lamella with a smaller thickness and a narrower thickness distribution than those of the poly(ethylene-alt-propylene) lamella. A study by transmission electron microscopy tends to support this result.
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    SAXS investigations of isotactic polypropylene (IPP) fibres mass coloured with organic pigments (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 715-720 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The effect of selected organic pigments on the supermolecular structure of isotactic polypropylene (IPP) fibre has been investigated. For the present work, three organic pigments of different molecular and supermolecular constitution were selected. Undrawn fibres with a minimal technological degree of drawing and fibres at draw ratios of 2, 4 and 5 were examined. The supermolecular structure was explored using small-angle X-ray scattering (SAXS). From the SAXS patterns the one-dimensional intensity function and the correlation function were determined. The parameters characterizing the supermolecular structure of the fibre, i.e. long period and invariant, were assessed. It was found that a lamellar structure develops during fibre formation. A regular lamellar structure is formed irrespective of the presence of pigments. On drawing fibres the high regularity of the lamellar structure decreases. In the drawing process the pigments are at the origin of micropore formation.
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    URL: http://dx.doi.org/10.1107/S0021889891000808
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    Small-angle neutron scattering study of sodium alkyl sulfate mixed micelles (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 747-752 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Sodium (octyl + decyl) and (octyl + dodecyl) sulfate mixed surfactant solutions containing the two solutes in a 1:1 proportion were studied by small-angle neutron scattering. The measurements were carried out at different concentrations and temperatures. For mathematical reasons it was not possible to determine the composition of mixed micelles through a least-squares fitting procedure, and therefore Clint's theory assuming ideal mixing of the components was used to calculate the monomer concentrations and the composition of micelles. With the calculated composition, two-shell spherical and ellipsoidal shape models were fitted to the experimental scattering curves. Except for the (octyl + dodecyl) sulfate micelles at higher concentrations, the best fit was obtained by a spherical model. The aggregation number in the mixed systems obtained from the fit lies between the aggregation numbers of the two single-component constituent systems, but closer to that of the longer chain and shows strong concentration and temperature dependence. The fractional charge of the mixed micelles was found to be smaller than the fractional charge of the single-component ones.
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    First results from a new perfect-crystal small-angle scattering instrument using a bent comb-shaped analyzer crystal (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 562-567 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The use of a bent comb-shaped analyzer crystal in a perfect-crystal SANS instrument makes possible the simultaneous measurement of many points of the rocking curve by means of a one-dimensional position-sensitive detector. This design permits high-resolution measurements with much higher efficiency than standard techniques. Results from our prototype instrument, using seven reflecting plates, are in very good agreement with predictions based on the dynamic theory of neutron diffraction.
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    Microstructure of nanocrystalline TiO2 and Ni at different degrees of compactness (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 603-606 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The change of the microstructure of nanocrystalline TiO2 and Ni as a function of the compaction procedure was measured by small-angle neutron scattering. The scattering cross section is attributed to contributions from crystallites separated by interfacial regions and to voids as well as to correlations in the spatial arrangement of the different structural components. For Ni there is no drastic change in the scattering cross section for the compacted nanocrystalline solid compared with the as-prepared disperse material. For TiO2 the scattering cross section changes substantially during compaction, caused by changes in volume fractions and size distributions of the different components.
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    Investigation of single-phase glasses using small-angle X-ray scattering techniques (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 616-623 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The study of single-phase glasses by X-ray scattering experiments requires special techniques. Experimental methods and data evaluation procedures aimed at obtaining reliable scattering data in the range of small and intermediate scattering angles are described. These techniques have been applied to the study of the intermediate-range order of silica and phosphate glasses. For commercial silica glasses and for phosphate glasses, the zero-angle scattering was found to be a very suitable parameter to quantify the optical homogeneity. The zero-angle scattering of alkaline-earth metaphosphate glasses was analyzed in terms of the formalism of Bhatia & Thornton [Phys. Rev. B. (1970), 2, 3004–3012]. From the results, conclusions were drawn about the chemical short-range order. In magnesium phosphate glasses, the presence of small clusters of about 1 nm diameter was established.
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    URL: http://dx.doi.org/10.1107/S0021889891000456
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    Investigation of the interface between polymers: a comparison of scattering and reflectivity techniques (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 651-658 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: With the techniques of small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) the interfacial region between polymers forming a two-phase structure can be investigated. Various approaches are possible including the classical Porod analysis as well as the Fourier transform, sandwich or contrast-matching techniques. Their application for the determination of the interface width and profile between polymer phases is discussed. As an alternative method X-ray and neutron reflectometry from polymer layer systems has recently been introduced. It allows an accurate determination of various interfacial parameters provided a flat and smooth interface with sufficient contrast between the materials can be prepared. The techniques are compared and discussed with respect to the information which is obtained on the interfacial region of polymers.
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    SANS and SAXS study of block copolymer/homopolymer mixtures (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 672-678 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The lateral and vertical components of the radius of gyration for a single block copolymer chain and those of a single homopolymer chain in the lamellar microdomain space formed by a mixture of diblock copolymers and homopolymers were investigated by means of small-angle neutron scattering (SANS) and the microdomain structures by small-angle X-ray scattering (SAXS). The homopolymers whose molecular weights are much smaller than that of the corresponding chains of the block copolymers were used so that the homopolymers were uniformly solubilized in the corresponding microdomains. The SANS result suggests that the homopolymer chains in the microdomain space as well as the block copolymer chains are more compressed in the direction parallel to the interface and more stretched in the direction perpendicular to the interface than the corresponding unperturbed polymer chains with the same molecular weight. On increasing the volume fraction of the homopolymers the thickness of the lamellar microdomains increases. The block copolymer chains were found to undergo an isochoric affine deformation on addition of the homopolymers or with the change of the thickness of the lamellar microdomains.
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    URL: http://dx.doi.org/10.1107/S0021889890014212
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    Study on interdiffusion of polystyrenes of high molecular weight by SANS (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 665-671 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The interdiffusion coefficient Dint of polystyrenes of different molecular weights has been measured. The small-angle neutron scattering (SANS) intensity from a sandwich-like sample consisting of alternating deuterated and protonated films is determined as a function of time and analysed with respect to Dint. In the symmetrical case both components have the same molecular weight and interdiffusion coefficients may be scaled according to the reptation theory D ̃M−2. The WLF (Williams–Landel–Ferry) temperature behaviour is observed. In the asymmetrical case using low- and high-molecular-weight polystyrenes, the interdiffusion is dominated by the faster-moving species. The fast-mode diffusion theory best describes the result. The influence of a non-zero Flory-Huggins interaction parameter χ between deuterated and non-deuterated material has been taken into account showing a significant slowing down for the high-molecular-weight material.
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    Decay of a shear-induced phase transition on a micellar solution measured by time-dependent small-angle neutron scattering (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 740-746 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Transient small-angle neutron scattering (SANS) experiments on sheared aqueous surfactant solutions of trimethyl(tetradecyl)ammonium salicylate (TTMA-Sal) are reported. A 0.005 M solution without shear shows a weak correlation peak. For steady shear rates above a threshold value of Γ = 50 s−1 the scattering pattern shows an abrupt increase in anisotropy which is related to a shear-induced structure transition. The analysis of the anisotropic pattern reveals the existence of two types of micelle: short rodlike micelles which are weakly aligned and very long rodlike aggregates which are strongly aligned and which are only present for Γ above the threshold value. We report results on transient SANS measurements in which the shear rate was changed stepwise from a value of 400 s−1 to zero. It is found that the smaller micelles are randomized in orientation, whereas the longer ones do not change orientation at all but their concentration vanishes. The number of surfactant molecules bound in the smaller micelles (type I) increases with time, whereas the number of surfactants bound in the larger ones (type II) decreases. The sum of both remains constant. The number of surfactant molecules bound in type II micelles decays exponentially with a half life of T1/2 = 1.7 (1) s.
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    Small-angle X-ray scattering study of cordierite sol–gel synthesis (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 765-770 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The structure of ceramic materials in the size range of a few nanometres to a few tens of nanometres is closely related to the structural features of the precursor. Here the nanostructural development of a cordierite (2MgO–2Al2O3–5SiO2) material is studied by SAXS during its processing by a sol-gel route. Homogeneous alcogels were prepared at 298 K by hydrolysis – condensation of a mixture made of Si(OC2H5)4, sec-Al(OC4H9)3, Mg(NO3)2, water and alcohol. The polymeric nature of the mechanism is evidenced. The final size and internal structure of the particles depend on the quantity of water used for hydrolysis. In the gel state, particles of 7 or 8 nm in size exhibiting a mass fractal structure with D = 1.9 are observed. Xerogels resulting from classical drying were powdered. Firing of pellets leads to porous solids. The small-angle scattered intensity grows strongly and the Porod plot shows a linear behaviour with a slope of −3.5. Sintering to full density is very difficult. Aerogels obtained by supercritical drying consist of primary homogeneous units of about 2 nm in size, attached into volume fractal aggregates (D = 1.8). The aerogels exhibit a dramatically improved sintering ability. Full dense glasses are obtained at temperatures less than 1273 K and fine-grained glass ceramics without any nucleating agent.
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    Atomic accessible and contact surfaces as restraints in the Hendrickson & Konnert refinement program (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 941-946 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A computer algorithm is presented for calculating and, if required, optimizing the extent of atomic areas in a molecule that are accessible to the solvent or in contact with non-solvent atoms either from the same or from another molecule. The algorithm has been implemented as new restraints in a modified version of the least-squares refinement program of Hendrickson & Konnert [In Computing in Crystallography (1980), edited by R. Diamond, S. Ramaseshan & K. Venkatesan, pp. 1301–1325. Bangalore: Indian Academy of Sciences]. Information on the correctness of atomic interactions in a given configuration can thus be used either as added data during the crystallographic X-ray refinement or, independently, in the analysis and modeling of molecular structures. The algorithm appears well suited for studying the structure and interactions of proteins and nucleic acids.
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    RIBBONS 2.0 (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 958-961 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The program RIBBONS 2.0 allows real-time viewing of solid shaded ribbon models of macromolecules. The primary features of the software are the ability to create a wide variety of styles of ribbon drawings interactively and to toggle between various coloring schemes chosen to reflect assorted geometrical and biochemical properties. Spheres, cylinders, dots, polygons and text are also supported. The auxiliary programs included make RIBBONS 2.0 a powerful tool for visual structural analysis as well as for presentation graphics. The program is currently available only for the Silicon Graphics 4D series of workstations. A port to the Evans & Sutherland ESV workstation employing PEX is under development.
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    Potassium titanyl phosphate, KTiOPO4. I. Experimental investigation of optical gyration, absolute optical chirality and twinning (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 963-967 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The optical gyrations of a domain-free section and of a twinned section of the nonlinear optical crystal KTiOPO4 have been measured using a high-accuracy universal polarimeter. An optical gyration at 6328 Å equivalent to an optical rotation of +22° mm−1 together with a significant circular dichroic contribution was found in the domain-free ({\bar 2}10) section whereas equivalent rotations varying between +14 and −20° mm−1 were found in different regions of the twinned section. The absolute indices of the faces of the samples and the existence of twinning in the second section have been established using X-ray anomalous scattering. The regions of opposite optical chirality in the twinned sample have been shown to correlate with those of opposite structural chirality. The results are used to show that the twinning operation in this KTiOPO4 crystal must be one of the twofold rotations 2[010] or 2[100].
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    Crystallographers (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 973-973 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    URL: http://dx.doi.org/10.1107/S0021889891009020
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    Resolution correction for surface X-ray diffraction at high beam exit angles (1993)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 26 (1993), S. 687-696 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Owing to the two-dimensional periodicity of a superstructure on the crystal surface, the intensity in reciprocal space is continuously distributed along rods normal to the sample surface. The analysis of rod scans in surface X-ray diffraction provides information about the structure parameters normal to the sample surface. For high resolution to be achieved, the measurements must extend to momentum transfers q⊥ that are as large as possible. At large exit angles, the conventional Lorentz factor must be modified to take account of the finite aperture of the detector and the continuous intensity along the lattice rod. For two types of Z-axis diffractometer used in surface X-ray crystallography, an analytical expression for the resolution correction of rod-scan intensity data has been developed. It takes into account an anisotropic detector resolution T(ΔΘ, ΔΦ), the finite width of the diffracted beam and the primary-beam divergence parallel to the sample surface, Δτ. The calculation of the convolution functions is simplified by a projection onto the q⊥ = 0 plane. The effects of different detector settings and the influences of the primary-beam divergence and the sample quality on the measured intensity are demonstrated for several examples.
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    A personal-computer-controlled single-crystal diffractometer (1993)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 26 (1993), S. 728-729 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A four-circle diffractometer system has been built around the Huber model 5042. The scintillation detector and associated electronics were assembled from commercially available standard modules. A comprehensive control program has been developed. It runs on a cheap personal computer that also incorporates a fast multichannel scaler board for automatic histogram production from continuous or step intensity scans. The software can handle the complete unit-cell determination and data collection in an automatic mode but for the experienced user who wishes to tailor the experiment to his or her particular needs, there are more than 100 commands available.
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    ORTEX – an interactive version of ORTEP for use on a PC (1993)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 26 (1993), S. 752-752 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    URL: http://dx.doi.org/10.1107/S0021889893005576
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    REPLACE, a suite of computer programs for molecular-replacement calculations (1993)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 26 (1993), S. 748-751 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A suite of computer programs (REPLACE) for crystal-structure determination by the molecular-replacement method has been developed. It currently includes a general (locked) rotation-function program (GLRF) and a translation-function program (TF). The rotation-function program can carry out ordinary as well as locked self- or cross-rotation-function calculations. It can also optimize non-crystallographic symmetry parameters based on the maximal electron-density overlap of the subunits related by the non-crystallographic symmetry. The translation search can be based on R-factors, correlation coefficients, Patterson correlation and electron-density-correlation criteria. The packing of the molecular structure in the unit cell can be checked as well.
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    Characterization of an image-plate detector used for quantitative small-angle-scattering studies (1993)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 26 (1993), S. 763-773 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: This paper describes the characterization of an image-plate readout system used to calculate small-angle-scattering intensities as cross sections per unit volume. The raw data are the latent phosphorescent excitations stored on an image plate. Self-decay, self exposure, resolution, smearing, dynamic range and sensitivity are measured. Preliminary experiments show that an inexpensive neutron-imaging system can be obtained when the plates are placed behind a suitable neutron-to-X-ray converter.
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    URL: http://dx.doi.org/10.1107/S002188989300487X
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    The half-widths of Bragg intensity profiles measured with a triple-crystal diffractometer at a synchrotron-radiation source. I. Derivation of a simple expression for the full width at half-maximum (1993)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 26 (1993), S. 753-755 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: On the basis of the expressions given by Rossmanith [Acta Cryst. (1992), A48, 596–610; (1993), A49, 80–91], a simple approximation is derived for the half-widths of Bragg intensity profiles measured with a triple-crystal diffractometer at a synchrotron-radiation source. This new formula facilitates insight into the effects of four parameters – divergence, wavelength spread, mosaic spread and mosaic block size – on the widths of the profiles.
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    Electron diffraction from phospholipids – an approximate correction for dynamical scattering and tests for a correct phase determination (1993)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 26 (1993), S. 778-786 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An approximate experimental correction of electron diffraction intensities from an epitaxically crystallized phospholipid bilayer for dynamical scattering is described. This correction, which is useful for certain low-angle centrosymmetric data sets, compares intensities recorded at high and low electron-accelerating voltages to ascertain which reflections are most affected by n-beam interactions. When applied to experimental intensity data from 1,2-dihexadecyl-sn-glycerophosphoethanolamine (DHPE), the correction facilitates a direct phase determination based on the probabilistic estimate of three-phase invariants because a more accurate estimate of the hierarchy of |El| values is obtained. When a multisolution technique is used, incorporating algebraic unknowns for certain phase values, the best phase assignment can be assessed by comparison of the single convolution of phased structure factors to the observed structure-factor magnitudes for the low-voltage data. This approach exploits an approximate analogy made earlier by Moodie between the Sayre equation and the phase grating series and is valid as long as the single convolution adequately models experimental low-voltage data (a condition favored by light-atom structures in a low-angle region of reciprocal space). In real space, the correct structure can also be readily identified as the one having the smoothest density profile.
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    Structure-refinement program for disordered carbons (1993)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 26 (1993), S. 827-836 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An automated structure-refinement program has been developed for X-ray powder diffraction data collected on disordered carbons. The program minimizes the difference between the observed and calculated diffraction profiles in a least-squares sense by optimizing model parameters analogously to the popular Rietveld refinement method. Unlike the Rietveld method, which is designed for crystalline materials, this program allows the quantification of the finite size, strain and disorder present in disordered carbon fibers and cokes. For example, the structural model used includes the probability of a random translation parallel to adjacent carbon layers as a refinable parameter describing turbostratic disorder. Other parameters are used to describe finite size, fluctuations in the spacing between adjacent layers, average lattice constants, background and other important quantities. The structural model, combined with the refinement program, acceptably describes the diffraction patterns from disordered carbons such as pitch heated near 823 K, cokes, fibers, heat-treated cokes and synthetic graphite.
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    Improved calibtration curve for the Sm2+:BaFCl pressure sensor (1993)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 26 (1993), S. 843-845 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The pressure sensor proposed by Shen, Gregorian & Holzapfel [High Press. Res. (1991), 7, 73–75], based on the pressure-dependent shift of the luminescence line due to the 5D0−7F0 electronic transition of Sm2+ in a matrix of BaFCl, has been tested in a diamond-anvil cell and calibrated against the R1−R2 doublet shift of ruby and the known NaCl equation of state, in the pressure range between 0.0001 and 4.3 GPa. The parabolic dependence of the shift from the pressure can be approximated by the equation Δ(nm) = 1.46P − 0.047P2, where the shift, Δ, is in nm and the pressure, P, in GPa. The estimated error in the pressure measurements is 5%. The Sm2+: BaFCl luminescence sensor can be advantageously used in the low to moderate pressure range (0.0001–5 GPa or more).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889893006120
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    Education and Teaching in Crystallography. Call for papers (1993)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 26 (1993), S. 846-846 
    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/S002188989309956X
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  • 78
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    Editorial (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 27 (1994), S. 1-1 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889893011720
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  • 79
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    Standard stereographic diagrams and indexing of X-ray Laue diffraction spots of an icosahedral quasicrystal (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 27 (1994), S. 13-19 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: White-beam synchrotron-radiation X-ray topographs of the Al62Cu25.5Fe12.5 icosahedral quasicrystal (IQC) have been taken for different specimen orientations. Standard stereographic projection diagrams along the two-, three-, and fivefold zone axes of the IQC have been calculated by the cut-and-projection method. The total structure factor S(g||) has been calculated with the simple lattice model for each reciprocal vector g|| with indices ni* lying in the range −8 ≤ ni* ≤ 8 and reflections with the highest S(g||) values have been selected to simulate the geometric distribution of the Laue spots for a given incident-beam direction. On the basis of standard diagrams of simulated Laue patterns, all the strong diffraction spots have been indexed successfully. For the specific experimental arrangement and the characteristics of the synchrotron-radiation source, the mean intensities of the diffraction spots have been calculated and are in agreement with the experimental ones.
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  • 80
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    Interpretation of the diffuse scattering close to Bragg peaks by X-ray topography (1993)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 26 (1993), S. 812-819 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Perturbations from crystal perfection will result in diffuse X-ray scattering, which can be imaged by topography to yield defect information without the swamping contribution of perfect-crystal scattering. This paper illustrates the importance of the probe shape for obtaining topographic images in this diffuse region not only to aid interpretation but to isolate the contributors to this scattering. The diffuse scattering in the vicinity of the Bragg peaks of GaAs, Si and Ge substrate crystals has been mapped to very high resolution and the diffuse scattering has been imaged by topography. It was found that the majority of the scattering emanates from surface damage and dislocations and not point defects or thermal diffuse scattering (TDS). These latter two components are found to be second-order effects in general and are only just discernable as a very weak background intensity in highly perfect crystals. This topography method is very sensitive to surface damage. This is because the associated diffuse scattering close to a Bragg peak can be used to form an image. Therefore, this relatively intense scattering provides a topograph within a few hours for assessing substrate-surface quality. The sensitivity of the method is illustrated with images of surface defects and dislocations in very perfect semiconductors. A procedure for measuring the diffuse scattering emanating from microdefects is also presented.
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    URL: http://dx.doi.org/10.1107/S0021889893006259
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  • 81
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    Crystallographers (1993)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 26 (1993), S. 846-846 
    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/S0021889893010672
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  • 82
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    A fast and portable microspectrophotometer for protein crystallography (1993)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 26 (1993), S. 839-842 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Spectroscopic measurements on crystals during X-ray data collection provide additional information on the composition of the crystal and can be used in the interpretation of structural data. This paper describes a portable microspectrophotometer to obtain UV–visible–near-IR spectra from single crystals during X-ray measurements. The instrument consists of a deuterium lamp, optical fibres, a pair of mirror lenses and a monochromator equipped with a photodiode array detector. Spectra can be recorded in short periods of time (a few milliseconds) from a measurement area of 0.10 mm diameter or smaller. The device can be used to monitor spectral changes in crystals during time-resolved X-ray experiments so that the X-ray camera can be triggered at the right moment as determined by the spectrum, thereby eliminating much of the present guesswork from such studies.
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    URL: http://dx.doi.org/10.1107/S0021889893005552
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  • 83
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    New Commercial Products (1993)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 26 (1993), S. 847-848 
    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/S0021889893099558
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  • 84
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    Small-angle X-ray scattering of systems with inhomogeneous particles (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 27 (1994), S. 20-24 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Stabilization procedures are used to deduce the distance distribution function p(r) for the specific case of inhomogeneous particles where the scattering curve I(q) is dominated by a peak resulting from the particle form factor. The system sodium dodecyl sulfate (SLS)/water micellar solution is studied by small-angle X-ray scattering for low concentrations (up to 9 wt% of SLS). Subsequent computation of the electron-density distribution ρ(r) from the function p(r) confirms the existence of micellar anisometry, which is also deduced from Dmax values. The modelling of ρ(r) by two- and three-step functions is discussed; both give reasonable agreement with the p(r) function.
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    URL: http://dx.doi.org/10.1107/S0021889893006247
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  • 85
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    A consistent formalism for partial structure functions (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 27 (1994), S. 25-28 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The structure of an amorphous binary system can be described by three partial structure functions and their Fourier transforms relating to the atomic interactions. The experimental total function is the weighted sum of the partials. Two different formalisms, the Faber–Ziman and Ashcroft–Langreth, are generally applied for expressing the weights. This paper suggests a third formalism, created by taking into consideration the physically established features of both of the other formalisms. It is free from the difficulties that may arise when these formalisms are used.
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    URL: http://dx.doi.org/10.1107/S0021889893006284
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  • 86
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    High-resolution electron-microscopic studies of the polymorphs in Ag2±δSe films (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 27 (1994), S. 140-145 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The polymorphs that appear in the low-temperature phase of silver selenide have been studied by high-resolution electron microscopy. The specimen films are intentionally prepared with excess silver or selenium over stoichiometric composition by flash evaporation, as depositing carbon films on both sides of the specimen films to protect them from selenium sublimation and to maintain the composition throughout the heat treatment. It is shown that four different types of low-temperature phase exist: tetragonal (a = 6.98, c = 4.96 Å) for a metastable phase only formed with a small grain size of less than 50 nm; face-centred cubic (a = 10.9 Å) for a non-stoichiometric phase with excess silver; monoclinic (a = 7.05, b = 8.17, c = 4.34 Å, α = 101.0°) for a non-stoichiometric phase with excess selenium; and orthorhombic (a = 7.05, b = 7.82, c = 4.34 Å) for the stoichiometric stable phase. The topotactic relations between the orthorhombic and monoclinic types are found to be fully coherent, having the same a and c lattice parameters.
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  • 87
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    New methods for alignment of instrumentation for residual-stress measurements by means of neutron diffraction (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 27 (1994), S. 164-176 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Adequate alignment of instrumentation and specimens is imperative for the successful performance of residual-stress measurements by means of neutron diffraction. This paper presents a number of alignment methods that enable the user to align reproducibly a stress-measurement setup and a specimen positioned therein. Most of these methods employ the position and the direction of the incident neutron beam as their primary source of geometric reference. A mathematical description for each of the proposed alignment steps is given, which makes the alignment quantitative and enables quantitative assessment of the alignment quality after each alignment step. Examples from actual practice show that the alignment quality that can be achieved using these methods is better than 0.05 mm for translations and better than 0.05° for rotations.
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    URL: http://dx.doi.org/10.1107/S0021889893007605
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  • 88
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    Remarks on four-circle angle calculations for surface diffraction (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 27 (1994), S. 195-197 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Corrections are presented to the angle calculations in surface diffraction [Mochrie (1988). J. Appl. Cryst. 21, 1–3] based on ψ rotation for four-circle diffractometers (Philips PW1100, Seifert XRD3000-S).
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  • 89
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    Two open-flow cryostats for macromolecular crystallography (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 27 (1994), S. 133-139 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Two open-flow cryostats for macromolecular crystallographic studies, which make it possible to freeze macromolecular crystals very rapidly and maintain them for long periods of time at reduced temperatures, have been constructed. Both systems avoid the use of opaque shrouds and hence permit monitoring of the optical properties of protein crystals at all temperatures. The first uses a cold-gas stream derived from boil-off of liquid nitrogen, with a surrounding warm-gas stream, and covers a temperature range of 80 K to room temperatures. The second uses a cold-gas stream derived from boil-off of either liquid helium or liquid nitrogen to cover a temperature range of 10 to 70 K or above 80 K, respectively. Special care has been taken to make it possible to switch back and forth between the two cryogenic liquids in routine operation. The temperature stability of the cold-gas stream is ±0.5 K, which is achieved by controlling both the flow rate of the gas stream and the power of a heater within the cold-gas stream prior to its exit from the nozzle. The liquid helium consumption is less than 21 h−1 at a working temperature of 40 K.
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  • 90
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    High-resolution diffraction at synchrotron sources: correction for counting losses (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 27 (1994), S. 159-163 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The operating schedules of synchrotron sources encourage relatively rapid data collection. Consequently, very high count rates may be met in powder diffraction experiments and high-resolution single-crystal studies. A rigorous treatment of the losses due to pulse pile-up is given, as well as a discussion of possible losses due to windowing. The code for a simple correction algorithm is provided and used to illustrate the effect of losses on the intensities of two of the reflections in the powder spectrum of cimetidine.
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    URL: http://dx.doi.org/10.1107/S0021889893014141
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    Structure of electrified interfaces edited by J. Lipkowski and P. N. Ross (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 27 (1994), S. 131-132 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    URL: http://dx.doi.org/10.1107/S0021889893011410
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  • 92
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    Growth of crystals. Vol 19. edited by E. I. Givargizov and S. A. Grinberg (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 27 (1994), S. 204-204 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S002188989409967X
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  • 93
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    Bent-crystal monochromator for 150 keV synchrotron radiation (1992)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 25 (1992), S. 432-438 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The 220 reflectivity curve of a 4 mm thick Si crystal is measured in asymmetric transmission (Laue) geometry. The crystal is bent to a radius varying from 24 to 138 m, and the analyzer is a nearly perfect Si(220) crystal in non-dispersive (+, −) arrangement. The full width at half-maximum of the reflectivity curves varies from 61 to 10 μrad, while that of a flat perfect crystal is 1.2 μrad, and the observed maximum reflectivity is about 60%. The calculated value is even higher, exceeding 80%. The bent crystal is used as an inverse-Cauchois monochromator, where the source of radiation is on the focusing circle. The effect of the beam divergence on the energy bandpass is eliminated, leaving only the contribution of the reflectivity curve. This can be matched to the desired resolution of the experiment by the choice of the thickness and asymmetry angle of the crystal. Compton-profile measurements from Ag and Au foils are used for a comparison of different monochromators. The bent-crystal monochromator provides 50 times more flux than the perfect Si(220) crystal and a better energy resolution than heat-treated Si(220) or mosaic Ge(220) crystals.
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    A Laue diffractometer with δ geometry (1992)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 25 (1992), S. 440-443 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The Laue technique shortens the time required to measure integrated intensities for X-ray structure determination. The Laue diffractometer presented here is a δ-circle diffractometer equipped with an ordinary low-cost photomultiplier-scintillation-crystal combination. Stepper-motor control devices and the multichannel analyzer (MCA) were originally developed for this particular purpose. These components are equipped with efficient microprocessor technology. A personal computer with graphic facilities is used for processing. Using special procedures in the analysis and the measurement of data, the disadvantages of a scintillation counter may be avoided or reduced.
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    URL: http://dx.doi.org/10.1107/S0021889891015157
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    FOURDEM: a program written as an aid to teaching the elements of Fourier synthesis and other crystallographic concepts (1992)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 25 (1992), S. 443-447 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A program is described which demonstrates in two dimensions the principles of Fourier synthesis. There are two versions of the program, written in Absoft Fortran for use on a Macintosh II computer: a manual version in which the student can type in values of h, k, |F| and phase angle φ, and an automatic version in which a file of prepared input data can be used. The program can be used to demonstrate the meaning of Miller indices; the relationship between the (hkl) planes and the diffraction pattern; the meaning of phase; Fourier summation; Patterson functions; difference Fourier synthesis; heavy-atom methods of phase determination etc.
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    URL: http://dx.doi.org/10.1107/S0021889891013389
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    DIFRAC, single-crystal diffractometer output-conversion software (1992)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 25 (1992), S. 455-459 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Software is described that converts single-crystal diffractometer output files as produced by manufacturers' software into a standardized instrument-independent form consisting of a clear, complete, well documented record of the sample and the diffraction measurements performed upon it. Information not already available in the manufacturers' diffractometer files is obtained in an interactive question- and-answer session. The software is written in a modular way. Available modules can deal with Enraf–Nonius CAD-4, Philips PW1100 and Siemens P21 single-crystal diffractometers and produce output in CIF or SCFS format.
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    URL: http://dx.doi.org/10.1107/S0021889892000384
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    MRIA - a program for a full profile analysis of powder multiphase neutron-diffraction time-of-flight (direct and Fourier) spectra (1992)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 25 (1992), S. 447-451 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The paper describes a universal program MRIA for the full profile analysis of powder neutron-diffraction time-of-flight direct and Fourier spectra. The minimum configuration of MRIA, analysing up to four spectra, four phases, 500 Miller indices for every phase and 100 independent atoms, can run on an IBM PC-AT or any compatible. The extended variant of the program, analysing data of larger size, runs on a MicroVAX computer. Part of MRIA, providing necessary service functions for a PC user, is written in TurboPascal 6.0. The basic programs of MRIA are written in standard Fortran77 and can be compiled by RMFORT or MSFORT77 and by an NDP compiler on a 32 bit PC.
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    URL: http://dx.doi.org/10.1107/S0021889891013122
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    Software and methods for precise X-ray analysis (1992)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 25 (1992), S. 451-454 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The software package PPXA (programs for precise X-ray analysis) is described, which provides crystallographers with increased precision and reliability of the results of X-ray analysis. The package includes programs for: testing the quality of an automatic four-circle X-ray diffractometer before X-ray experiments; optimization of X-ray diffraction experiments; preliminary processing of experimental data; precise structure analysis up to electron density distribution. The programs for diffractometer testing allow the experimenter to check the stability and precision of the instrument, the homogeneity of the X-ray beam and the detector sensitivity. The programs for preliminary data processing include: corrections for absorption, taking into account the intensity distribution in the X-ray beam cross section; correction or elimination of the simultaneous reflection effect; background subtraction, correcting the effects of the scan-interval cut-off; correction for thermal diffuse scattering (TDS) for crystals in cases of both known and unknown elasticity constants. The programs for precise crystal structure refinement include options for the determination of primary- and secondary-extinction parameters, atomic coordinates, thermal-vibration parameters in harmonic and anharmonic approximations, occupation of atomic positions, atom-core and valence-shell occupation parameters. The programs were written for a MicroVAX-II computer with a VAX/VMS operating system and designed to work with CAD-4 diffractometers and the SDP-Plus software package. A suitable dialogue with a menu system and detailed user's instructions are available.
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    URL: http://dx.doi.org/10.1107/S0021889891014243
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    X-ray texture analysis of thin films by the reflection method: intermediate regime in defocusing corrections (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 27 (1994), S. 278-282 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: This paper gives the angular domains of validity for corrections of experimental data obtained from the texture analysis of thin films, multilayers and covered substrates by the Schulz reflection technique. The behaviours of defocusing curves versus material constants are given as examples and their effects on correction curves are shown. The correction formulas for characteristic types of multilayers are also deduced and are illustrated for one example.
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    URL: http://dx.doi.org/10.1107/S0021889893008611
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  • 100
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    Collection and analysis of powder diffraction data with near-constant counting statistics (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 27 (1994), S. 385-392 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The concept of a variable-counting-time (VCT) strategy for use in Rietveld analysis of X-ray powder diffraction data was introduced by Madsen & Hill [Adv. X-ray Anal. (1992), 35, 39–47]. This strategy is based on a function that increases the counting time used at each step in the scan in a manner that is inversely proportional to the decline in reflection intensity that inevitably results from the combined effects of Lp factor, scattering factor and thermal vibration. The present work extends the VCT function to include the effects of reflection multiplicity, cylindrical-sample (capillary) absorption and monochromator polarization. The new algorithm has been incorporated into a PC computer program and applied to the collection of data from samples of LaB6, tourmaline, forsterite and boehmite. Subsequent analysis of the data using the Rietveld method has shown that VCT data can produce more accurate atomic coordinates and site occupancies, lower residual 'noise' in difference Fourier maps and more stable refinement of `light' atoms.
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    URL: http://dx.doi.org/10.1107/S0021889893008593
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