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  • 1
    Electronic Resource
    Electronic Resource
    A study of second-order thermal diffuse X-ray scattering effects and the elastic properties of cubic single crystals (1970)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 26 (1970), S. 354-358 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The elastic constants of certain single crystals may be obtained by the measurement of thermal diffuse X-ray scattering variation in regions close to reciprocal-lattice points. A method has been given which allows for second-order contributions to the total diffuse intensity by use of a least-squares procedure. The refinement was simplified by equating two functions, each depending on the elastic properties of the crystal, the nearby lattice point to the positions of observation and the direction along which the intensity variation is measured. For cubic crystals, there is an exact equality between appropriate powers of these functions for several important crystallographic directions, while for other directions some approximation results. The present paper includes a simple method of allowing for the deviation from equality in the latter cases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739470000840
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  • 2
    Electronic Resource
    Electronic Resource
    Structure factor amplitudes from thermal diffuse scattering measurements (1971)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 27 (1971), S. 256-259 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A method is proposed, for certain single crystals, of estimating the structure factor amplitudes corresponding to Bragg reflexions with strong to medium integrated intensities from measurements of the thermal diffuse X-ray scattering in regions of reciprocal space close to the appropriate lattice points. The values obtained conventionally from integrated Bragg intensities are often subject to considerable error due to extinction effects. The thermal diffuse scattering, being incoherently scattered and of a relatively weak intensity, would appear to be less likely to be affected by primary and secondary extinction. The structure factor amplitudes (or correction factors for those found from Bragg measurements) are obtained from the observed scattering data by a least-squares refinement method. Procedures are suggested for use where measurements are made on (i) a relative scale, (ii) an absolute scale, with respect to the direct beam intensity. The method is illustrated by application to some single-crystal data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739471000597
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  • 3
    Electronic Resource
    Electronic Resource
    Correction for second-order diffuse X-ray scattering in the determination of the elastic constants of crystals (1968)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 24 (1968), S. 336-338 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A new and improved method of allowing for second-order thermal diffuse X-ray scattering, close to a reciprocal-lattice point, is proposed; an appropriate equation for first- and second-order contributions is matched, by the method of least-squares, to the experimentally measured scattering data. A program was written for the I.C.T. 1905 computer and some K[ABC]hkl values for KCl were compared with those previously reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739468000665
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  • 4
    Electronic Resource
    Electronic Resource
    On the contribution of thermal diffuse X-ray scattering to the integrated Bragg intensities of single crystals (1969)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 25 (1969), S. 627-631 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The effect of including first-order and second-order thermal diffuse scattering contributions on the theoretical treatment for integrated Bragg intensities of single crystals is given for crystals belonging to any crystal system and with any number of atoms per unit cell. With certain restricting approximations and assumptions, the modified integrated intensity is found to be a product of the Bragg scattering and a factor, exp (C sin2 θ0/λ2), where C is a simple function of the X-ray wavelength, the temperature, the angular peak-width, and a quantity related to the elastic properties of the crystal. For cubic crystals, C is found to be approximately constant and thus confirms the result obtained by Nilsson (1957, Ark. Fys. 12, 247) for simple cubic crystals. The theory is applied to Al and KCl crystals, and calculated values for the ratio of uncorrected to corrected integrated Bragg intensities show reasonable agreement with some experimental values obtained using the Mössbauer effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739469001392
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  • 5
    Electronic Resource
    Electronic Resource
    Determination of molecular orientations in cubic ND4NO3 by multipole analysis (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 591-597 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Rietveld's profile refinement method applied to the neutron powder diffraction data of cubic ND4NO3 cannot distinguish between the two best orientation models put forward by Shinnaka [J. Phys. Soc. Jpn (1959), 14, 1073-1083] for rigid NO-3. The direct multipole analysis of the nuclear smearing functions yields a model with the values B+ = 11.5 and B_ = 14.3 Å2 for the molecular Debye-Waller factors and 0.99 and 1.23 Å, for the N-D and N-O bond lengths with additional fourth-order multipolar coefficients to describe the deviations from molecular free-rotation. The fourth-order multipolar components are significant. They support the two equivalent orientations model for rigid ND+4 tetrahedra with librational amplitude (θ2)1/2 = 13.0°. While the fourth-order multipolar coefficient of NO-3 represents well the experimental information, its value cannot be explained by any rigid model for NO-3 but only by an octahedral statistical coordination. This rules out the eight-orientations model and gives a slight preference to the twelve-orientations model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S056773947900139X
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  • 6
    Electronic Resource
    Electronic Resource
    MORGUE, a neutron powder diffraction profile refinement program with control-file facility to include structural and rigid-body thermal-motion constraints (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 629-633 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A neutron powder profile refinement program, MORGUE, has been written to facilitate the (possible) inclusion of both structural and rigid-body thermal-motion constraints. MORGUE results from major code modification to the program EDINP [Pawley (1980). J. Appl. Cryst. 13, 630–633] to allow the introduction of constraint conditions from an input parameter file in most practical situations. This replaces the previous need to write constraint-specific sub-routines for each structural and thermal-motion model refined, with the consequent repeated requirement for some recompilation and linkage of the modular parts to form the new executable program. The code is written in (VAX/VMS) Fortran77 and the program has been run on a VAX 11/750 computer. Examples of its use are included.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889889008691
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  • 7
    Electronic Resource
    Electronic Resource
    POLISH: computer program for improving the accuracy of structure-factor magnitudes obtained from powder data (1993)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 26 (1993), S. 137-139 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A computer program, POLISH, is presented that improves the accuracy of the structure-factor magnitudes obtained from powder data. This offers a greater likelihood of success for structure determination by direct methods or Patterson techniques. Generally, the program will be used in conjunction with a unit-cell refinement program, but it may also be used independently. Accurate values of the unit-cell and peak-shape parameters are required, which may be conveniently obtained from the unit-cell-refinement program. The program is tested by application to ND4NO3 (V).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889892007611
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  • 8
    Electronic Resource
    Electronic Resource
    Crystal structure determination by neutron powder diffraction using structural and packing constraints (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 1005-1008 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: In the past, crystal structure determination of solids consisting of molecules (or atom groups) whose geometry and size are known approximately has often been attempted using neutron powder diffraction profile refinement techniques, but without inclusion of this information. A method of structure solution has therefore been developed to include it. The proposed method does not require a set of structure factors and thus avoids the problems encountered in separating peaks in a powder diffraction scan. A successful test was conducted with a previously determined (yet treated as unknown) crystal structure, where direct methods had failed to solve the structure due to incorrect peak separation. Two computer programs, MODEL and PARAM, that implement the method are described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889891006970
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  • 9
    Electronic Resource
    Electronic Resource
    PARSET and PARSYM - production of files for neutron powder structure refinement program MORGUE and solution/refinement program PARAM (1995)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 28 (1995), S. 65-66 
    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/S0021889894010630
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  • 10
    Electronic Resource
    Electronic Resource
    Approximations in refinement of elastic constant values from thermal diffuse scattering measurements (1971)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 4 (1971), S. 397-398 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The effects of approximations in the refinement of elastic constant values from thermal diffuse scattering measurements are considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889871007283
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