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  • 1
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1-1 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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  • 2
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 10-25 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A new computer program for on-line crystallographic analysis in transmission electron microscopy (TEM) is presented. The program is based on the fast on-line determination of single-crystal orientations from Kikuchi and spot patterns. Spot patterns, which are particularly useful in the case of highly deformed metals, are analyzed by a new digital image processing procedure. This procedure improves the precision and ease of the orientation measurement. The program permits the on-line measurement of glide systems characterized by the Burgers vector and the crystallographic line direction of dislocations and their glide planes. The determination of twin systems, based on the misorientation calculation for any crystal structure, is included as well. The possibility of determining the foil thickness permits the complete crystallographic characterization of interfaces. Finally, the program facilitates the discrimination of phases and includes the fit of the lattice parameters a, b and c from diffraction patterns. The new procedures are described in detail. Application examples are given for all functions.
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  • 3
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 26-34 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The non-destructive X-ray diffraction method is usually employed to evaluate stress states at the near surface of materials. In specific zones with high-stress gradients parallel to the surface, like welding joins, areas affected by lasers, or ball-bearing raceways, the classical measurement method is not particularly well suited, as the irradiation spot covers regions of varying stress according to its size. This leads to inaccurate stress evaluations. A new X-ray diffraction measurement and data treatment method is therefore proposed. It is based on longitudinal step-by-step scanning in a fixed direction of the surface. As the acquired data results from the convolution of local diffraction peaks with the incident-beam intensity, an accurate model of the true two-dimensional intensity distribution inside the spot has been developed. Firstly, the true shape and size of the irradiation area is defined. The distribution of the intensity received by the sample surface is then computed. The true local strains and stresses along the scanning direction are finally determined from the acquired peaks using an optimization through a least-squares fitting by a nonlinear function.
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  • 4
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: High-resolution X-ray diffractometry, absolute integrated intensity (ρ) measurements, diffuse X-ray scattering (DXS) and infrared (IR) absorption techniques were used to investigate the influence of oxygen on the structural perfection of high purity (resistivity of the order of 4 kΩ cm) float zone (FZ) grown (111) silicon single crystals. A multicrystal diffractometer set in (+,-,-,+) geometry, with Mo Kα1 radiation, was employed. From the infrared measurements, the oxygen concentration in the sample was determined to be 1.3 × 1017 atoms cm^{-3}. High-resolution X-ray diffraction curves of the as-grown crystal had half-widths of ∼11 arcsec; the ρ value was 3.5 × 10^{-5} rad. To incorporate oxygen in a controlled manner into the specimens, they were annealed under dry oxygen ambient for 8 h in the temperature range 573–1373 K (in eight steps). Up to 723 K there was no appreciable change in oxygen content or in the degree of perfection. Annealing at temperatures (AT) 〉 873 K resulted in considerable increases in the oxygen content, as well as significant improvements in the degree of perfection. For example, as the level of oxygen increased from 1.3 × 1017 to 3.6 × 1017 atoms cm^{-3} for A_T=873 K, the values of half-widths and ρ decreased to ∼7 arcsec and 2.4 × 10^{-5} rad, respectively. However, annealing above 1273 K produced deterioration in lattice perfection. DXS measurements showed remarkable changes in the nature of point defects and their clusters with change in AT. Up to A_T=973 K, the defects were predominantly vacancy clusters. However, with AT in the range 1073–1273 K, the predominent defects were isolated interstitials. Further increase in AT led to interstitial cluster formation, which deteriorated the lattice perfection. This study clearly demonstrates that oxygen concentration in the range ∼3 × 1017 to 13 × 1017 atoms cm^{-3} leads to significant improvement in structural perfection of silicon single crystals.
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  • 5
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Methods for correcting specimen absorption in X-ray diffraction experiments, dedicated to two-dimensional area-detector systems and broad diffuse scattering phenomena, are implemented and tested. The respective transmission factors, in relation to the crystal or specimen shape, are applied to the intensity of every pixel of the two-dimensional detector. The pixel-wise approach allows for a fully quantitative treatment of continuous diffraction information, such as disorder diffuse scattering or scattering from amorphous materials, which is collected with a two-dimensional detector system. This is in contrast to routine data reduction, where the transmission factors are applied to the integrated Bragg intensities only. Furthermore, it is possible to assign different linear attenuation coefficients to the paths of the incident and scattered beams, as is desirable, for instance, in the case of X-ray holography with an internal resonant scatterer. Broad diffuse scattering data collected with synchrotron radiation and numerical calculations are used to study in detail the influence of experimental parameters on the accuracy of the pixel-wise absorption correction.
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  • 6
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 49-51 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A procedure for calculating the correct angle setting for a specific three-beam situation on a six-circle κ diffractometer is outlined. It is experimentally shown that interference profiles can be recorded using this approach. Limitations owing to mechanical constraints, with particular emphasis on the ability to measure Friedel-related triplets, are discussed.
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  • 7
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 64-70 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The thermal behaviour of a 30Li2O·70TeO2 glass was studied by use of an in situ high-temperature X-ray diffractometer equipped with a position-sensitive detector (PSD). The dynamical structural changes were also observed by differential thermal analysis (DTA) and differential scanning calorimetry (DSC) measurements. Differences and contradictions exist in previous studies related to the phase relation at high temperature, including the process of phase change. It is found that in the exothermic process after a glass transition between 553 and 623 K, an unknown phase of lithium tellurite (LT-X) crystallizes at first. At almost the same temperature, a minor component of vitreous TeO2 appears during decomposition of vitreous 30Li2O·70TeO2 of the initial phase. After that, the thermal changes of the lithium tellurite and the TeO2 components proceed independently. The LT-X phase converts to α-Li2Te2O5, and the vitreous TeO2 phase is followed by crystallization of an α-TeO2 phase. In the endothermic process between 673 and 793 K, the α-Li2Te2O5 phase transforms into a β-Li2Te2O5 phase and the minor crystalline α-TeO2 phase melts. Then, β-Li2Te2O5 incongruently melts to form Li2TeO3 and a molten TeO2 phase. Li2TeO3 continuously melts at around 763 K. The results show a possibility of reversible change between the α-Li2Te2O5 and the β-Li2Te2O5 phases.
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  • 8
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The development of the energy/angular dispersive diffraction setup, which can be used for anomalous diffraction, allows the collection of diffracted intensities around an absorption edge, either over a continuous energy range [for DAFS (diffraction anomalous fine structure) studies], or at discrete energies [for simultaneous MAD (multiwavelength anomalous diffraction) studies]. Used with a large two-dimensional detector and an oscillating single crystal, this setup allows simultaneous collection of many reflections for a given energy range. An integration procedure has been developed along with a program, DAD (dispersive anomalous diffraction), for the collection and analysis of the raw images, to yield finally data in the form I(h, k, l, λ) for all reflections. Wavelength calibration and intensity corrections are made during the integration process, and parameters that may be needed in later stages of the analysis are extracted and referenced within the integrated data. A general procedure to calculate the positions of diffracted reflections, for a monochromatic oscillation scan with a two-dimensional detector, when the incident beam is not perpendicular to the oscillation axis, is also described.
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  • 9
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The accuracy with which it is possible to determine atomic coordinates of light atoms at arbitrary positions using X-ray powder data alone is demonstrated. For this purpose use is made of synchrotron powder diffraction data obtained for an organic molecule, m-fluorobenzoic acid, consisting of ten non-hydrogen atoms (C7H5FO2). The results are compared with those of a single-crystal study on the same compound, and in particular the differences in bond lengths and bond angles are studied. The structure solution produced by direct methods is compared with the final result after the Rietveld refinement. The effect of performing the data collection at room temperature and at 100 K is also investigated. The bond lengths extracted from the powder data were found to differ from the single-crystal values by an average of 0.025 Å when data collected at room temperature were employed, and by 0.021 Å when using 100 K data. For the bond angles the corresponding values were 3.5 and 1.5°, respectively. With the low-temperature data it was possible to refine all atoms, including the hydrogen atoms, without restraints, whereas for the data collected at room temperature, strong restraints had to be used for the hydrogen atoms.
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  • 10
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 71-81 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The X-ray diffraction pattern of powdered 1-Cl-4-NO2-benzene was measured at several temperatures in order to characterize the structure of two different phases. For T 〈 282 K, the crystal array is ordered and exhibits P21 symmetry with two molecules in the unit cell; the observed lattice parameters at T = 190 K are a = 5.838 (4), b = 5.218 (3), c = 10.716 (5) Å and β = 96.43 (5)°. A molecular arrangement inside the unit cell which minimizes the crystalline packing energy was calculated and, in combination with the Rietveld method, was used to reproduce the observed diffraction pattern. The refined structure yields an excellent agreement with the experimental results and confirms a qualitative model previously suggested to explain the measured low-frequency Raman spectrum. The high-temperature phase is monoclinic, Z = 2 with a = 3.84 (1), b = 6.80 (1), c = 13.37 (1) Å and β = 97.4 (1)° at T = 290 K. As confirmed by a Rietveld refinement, this phase exhibits an orientationally disordered arrangement in which dipoles of equivalent molecules point along opposite directions. This leads to a statistically centrosymmetrical molecule and enables P21/c symmetry, in agreement with previous studies. The X-ray diffraction pattern also reveals an important increase of the background radiation which, in turn, exhibits a marked modulation of its intensity. On this basis, a simple analytical model has been developed to predict the angular dependence of diffuse scattering due to orientational disorder. The scope and limitations of this model are exhaustively discussed through a detailed comparison with the experimental results.
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