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  • 11
    Electronic Resource
    Electronic Resource
    Applications of High-Energy Synchrotron Radiation for Structural Studies of Polycrystalline Materials (1997)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 4 (1997), S. 147-154 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The large penetration power of high-energy X-rays (〉60 keV) raises interesting prospects for new types of structural characterizations of polycrystalline materials. It becomes possible in a non-destructive manner to perform local studies, within the bulk of the material, of the fundamental materials physics properties: grain orientations, strain, dislocation densities etc. In favourable cases these properties may be mapped in three dimensions with a spatial resolution that matches the dimensions of the individual grains. Imbedded volumes and interfaces become accessible. Moreover, the high energies allow better in-situ studies of samples in complicated environments (industrial process optimization). General techniques for research in this energy range have been developed using broad-band angle-dispersive methods, on-line two-dimensional detectors and conical slits. Characterizations have been made at the level of the individual grains and grain boundaries as well as on ensembles of grains. The spatial resolution is presently of the order of 10–100 μm. Four examples of applications are presented along with an outlook.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0909049597002021
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  • 12
    Electronic Resource
    Electronic Resource
    Accurate determination of strain tensors from small shifts of reflections measured on a four-circle diffractometer (1992)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 25 (1992), S. 372-376 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Formulas are given for the derivation of the changes in Bragg angles and the corresponding full asymmetric strain tensor from the shifts of reflections measured on a four-circle diffractometer. The effects of using either an ω- or a 2θ-scan mode are discussed. A least-squares program was written on the basis of the derived formulas and applied to data measured on the piezoelectric crystals of AgGaS2 under the influence of an external electric field. The obtained piezoelectric constants are in good agreement with values determined by conventional methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889891014164
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  • 13
    Electronic Resource
    Electronic Resource
    Modified counterweights and beamstop for the Huber 512 and 511.1 four-circle diffractometers (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 1072-1073 
    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/S0021889891008154
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  • 14
    Electronic Resource
    Electronic Resource
    Deconvolution of the two-dimensional point-spread function of area detectors using the maximum-entropy algorithm (1999)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 32 (1999), S. 683-691 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The maximum-entropy method (MEM) has been applied for the deconvolution of the point-spread function (PSF) of two-dimensional X-ray detectors. The method is robust, model and image independent, and only depends on the correct description of the two-dimensional point-spread function and gain factor of the detector. A significant enhancement of both the spatial resolution and the contrast ratio has been obtained for two phase-contrast images recorded with an ultra-high-resolution X-ray imaging detector. The method has also been applied to a Laue diffraction image of a protein crystal, showing an important improvement in both the peak separation of closely spaced diffraction peaks and the signal-to-noise ratio of medium and weak peaks. The principle of the method is explained and examples of its application are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889899003817
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  • 15
    Electronic Resource
    Electronic Resource
    Wide Dynamic Range Germanium Detector for Perturbation Crystallography (1996)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 3 (1996), S. 156-159 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An IR detector based on a cooled germanium photodetector has been tested for applications in X-ray diffraction. The detector can be used simultaneously in photon-counting mode and current mode giving a dynamic range from 〈 1 to 109 photons s−1. Since germanium is used as the photodetector, its efficiency at energies above 25 keV is much better than the silicon equivalents. The detector proved to be highly linear both in the low-flux region (〈 105 photons s−1) where photon counting is used and in the high-flux region (〉 105 photons s−1) where the detector is run in current mode. The response time of the detector is of the order of 1 μs, making it suitable for studies in perturbation crystallography, especially when coupled to a lock-in amplifier. As an example, the shift of a reflection of LiNbO3 induced by an external electric field was determined with the germanium detector and lock-in amplifier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0909049596005109
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  • 16
    Electronic Resource
    Electronic Resource
    Electric-field-induced structural changes measured with a CCD-coupled X-ray image intensifier (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1422-1429 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The conventional method to measure small induced changes in integrated intensity utilizes a zero-dimensional detector, which greatly limits the data collection speed. This paper shows that the use of an area detector in combination with an X-ray chopper decreases the data collection time significantly. A monochromatic diffraction setup using a charge-coupled device (CCD) detector coupled to an X-ray image intensifier was constructed and tested. The setup proved to be sufficiently stable to measure changes in integrated intensity well below 0.1%. Subsequently, a data set of a piezoelectric KD2PO4 crystal in an external electric field was collected. The data were merged to yield 77 unique reflections. The induced structural changes were determined by a least-squares refinement. The results agree very well with experiments in which a zero-dimensional detector was used. The major improvement is the decrease in data collection time by one order of magnitude, without any degradation of the data quality, offering new possibilities for this type of perturbation study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800013285
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  • 17
    Electronic Resource
    Electronic Resource
    Closed-cycle helium cryostat mount for the Huber 511.1 diffractometer circle (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 961-962 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Modifications to the high-stability mounting device for the closed-cycle helium cryostat as developed by Henriksen, Larsen & Rasmussen [J. Appl. Cryst. (1986). 19, 390–394] are described. They allow use of the cryostat on the smaller Huber 511.1 diffractometer circle with a smaller source-to-sample distance and reduced blind and collision zones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889891003485
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  • 18
    Electronic Resource
    Electronic Resource
    Towards extinction-free experimental diffraction data on Al2O3 (1998)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 54 (1998), S. 193-195 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Using 58 keV (0.214 Å) synchrotron radiation we have obtained virtually extinction-free data on Al2O3. Refinement of a multipole model against these data produced deformation densities of high quality, which compare well with theoretical maps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768197012949
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  • 19
    Electronic Resource
    Electronic Resource
    Molecular reorientation in an electric field as studied by single-crystal X-ray diffraction (1992)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 48 (1992), S. 113-120 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The molecular reorientation induced by an external electric field has been determined for the first time in order to obtain a microscopic understanding of the interaction between crystals and electric fields. Changes in scattering intensity are found when an electric field is applied parallel to the polar axis of a non-linear optical crystal of 2-methyl-4-nitroaniline (MNA), which has large piezoelectric constants [Paturle, Graafsma, Sheu, Coppens & Becker (1991). Phys. Rev. B, 43, 14683–14691]. The effect has been analyzed in terms of a change in cell parameters, a molecular rotation of 0.45 (5) × 10−2° about an axis nearly parallel to the electric field and a molecular translation of 0.19 (3) × 10−3] Å along the b axis. Since the orientation of the molecular dipole moment vector is unaffected, the piezoelectric contribution to the permittivity for this electric field direction is small. As expected, the centrosymmetric crystals of p-nitroaniline and p-nitropyridine N-oxide have no first-order converse piezoelectric effect and show no measurable change in X-ray scattering intensity under the influence of an external electric field of 2.2 × 106 V m−1. For the non-centrosymmetric crystals of 3-methyl-4-nitropyridine N-oxide, the effect is small, in agreement with the small value of the piezoelectric constants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767391008887
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  • 20
    Electronic Resource
    Electronic Resource
    The influence of an external electric field on the X-ray scattering of 2-methyl-4-nitroaniline, an organic crystal with nonlinear optical properties (1989)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 45 (1989), S. fc25-fc28 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The influence of an electric field on the X-ray scattering of the nonlinear optical organic crystal MNA (2-methyl-4-nitroaniline) has been studied, using a three-step pulsed alternating electric field. The field changes are synchronized with the gating to three different counting chains (the three-step modulation method). A field strength of 39 kV cm-1 induces 0.2% maximum variation in the integrated intensity and a small shift in Bragg angles (an inverse piezoelectric effect). A special electron density refinement method, which uses the differences between the zero- and applied-field intensities as observations, has been developed and applied in the interpretation of the results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767389005611
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