摘要:

A photographic Weissenberg camera has been constructed which can be mounted on the 2θarm of a four‐circle diffractometer. At a distance of 0.5 m from the sample the 2θresolution for a 100 μm crystal is 0.2 mrad (0.01°), allowing a high‐resolution mapping of reciprocal space at a synchrotron source in an efficient way. As sample experimental results, a study is presented of the streak system around the 111 reflection of a perfect germanium crystal and the detection of a minute phase transformation in a single‐powder grain of a high

ISSN:1600-5767    

DOI:10.1107/S0021889890004216

出版商:International Union of Crystallography    

年代:1990

数据来源: WILEY

摘要:

Bragg and diffuse scattering contributions to a reflection can be separated using the intensity dependence on the amplitude of transverse ultrasound excited in the crystal. The method is based on the fact that a weak ultrasound with wavelength equal to the extinction length suppresses almost completely the anomalous transmission of the coherent (Bragg) beam in a sufficiently thick absorbing crystal and does not affect diffuse scattering. Both parameters characterizing diffraction in a slightly imperfect crystal, the static Debye–Waller factor and the coefficient of additional absorption due to diffuse scattering, have been determined for a silicon crystal containing oxide precipitates after heat treatmen

ISSN:1600-5767    

DOI:10.1107/S0021889890004320

出版商:International Union of Crystallography    

年代:1990

数据来源: WILEY

摘要:

A best‐fitting version of the X‐ray diffraction method of Gehrke&Zachmann [Makromol. Chem.(1981).182, 627–635] for crystallinity determination, which is a modification of the method developed by Ruland [Acta Cryst.(1961).14, 1180–1185], is presented. The data, corrected and normalized to electron units (e.u.), are plotted asI(s)s2vs sand fitted by pseudo‐Voigt functions for the crystalline peaks added to a background scatteringIB(s)s2, withIB(s) = (1 −Xc)Iam(s) +Xc〈f(s)2〉[1 − exp(−ks2)], whereIamis the experimental intensity of a completely amorphous sample (also corrected and normalized to e.u.), 〈f(s)2〉 is the mean square atomic scattering factor in the material,Xcis the degree of crystallinity andkis a factor which includes either thermal or lattice disorder, wheres= 2(sinθ)/λ. The use of the scattering of the amorphous sample in this non‐integral form of the Ruland equations overcomes the problem, encountered with other procedures, of locating the continuous (background) scattering with accuracy. The degree of crystallinity and the disorder factor are supplied directly by the optimization process. Furthermore, the line broadening analysis which allows the determination of crystallite size is automatically obtained as a by product. Samples of polyethylene terephthalate (PET) with different degrees of crystallinity are investigated. The results are compared with those obtained by other methods which do

ISSN:1600-5767    

DOI:10.1107/S0021889890004939

出版商:International Union of Crystallography    

年代:1990

数据来源: WILEY

摘要:

Small‐angle neutron scattering measurements at various contrasts were performed on dilute colloidal silica dispersions in order to resolve the internal structure of the particles. The particles were prepared by outgrowth of a commercially available silica core, followed by an esterification of the surface silanol groups with stearyl alcohol. Variation of the scattering contrast was achieved by using mixtures of1H12‐ and2H12‐cyclohexane as dispersing medium. The scattering data were interpreted as originating from a polydisperse system of spherical three‐layer particles. Model parameters were optimized sequentially, applying an increasing number of constraints. Good agreement between experimental and calculated scattering curves is obtained, even at higherKvalues and low contrasts. In comparison with other particles in the same size range, these silica particles represent a very suitable model system for small‐angle scattering experiments at higher volume

ISSN:1600-5767    

DOI:10.1107/S0021889890005027

出版商:International Union of Crystallography    

年代:1990

数据来源: WILEY

摘要:

This paper contains information about the Riemannian structure of orientation space which is necessary for the analysis of the rotation rate field, which in turn describes some aspects of the plastic deformation of textured polycrystalline materials. The components of the metric tensor and the connection coefficients in the coordinates used in quantitative texture analysis are given. The relation between the vector components at symmetrically equivalent points and the relation between the frequently used vectors of infinitesimal rotations are presented. The solution of the continuity equation is given for the case of a constant rotation rate field during the deformation process.

ISSN:1600-5767    

DOI:10.1107/S002188989000512X

出版商:International Union of Crystallography    

年代:1990

数据来源: WILEY

摘要:

The accuracy of the Chebyshev expansion coefficients used for the calculation of attenuation correction factors for cylindrical samples has been improved. An increased order of expansion allows the method to be useful over a greater range of attenuation. It is shown that many of these coefficients are exactly zero, others are rational numbers, and others are rational fractions ofπ−1The assumptions of Sears [J. Appl. Cryst.(1984),17, 226–230] in his asymptotic expression of the attenuation correction factor are also exam

ISSN:1600-5767    

DOI:10.1107/S0021889890005258

出版商:International Union of Crystallography    

年代:1990

数据来源: WILEY

摘要:

A method for mounting single crystals in macromolecular crystallographic studies is described in which the crystal is suspended in a thin film. The film is formed from a mixture of the crystallization buffer and a hydrophilic viscous material, confined within a thin‐wire loop by surface tension. Compared with conventional crystal mounting methods, this method greatly simplifies and speeds the mounting procedure, is well suited to shock freezing and to optical monitoring of the crystals, deforms fragile crystals less and gives a lower and more uniform background in the X‐ray diffraction patte

ISSN:1600-5767    

DOI:10.1107/S0021889890005568

出版商:International Union of Crystallography    

年代:1990

数据来源: WILEY

摘要:

The integrated intensities measured in X‐ray single‐crystal high‐pressure structural studies using a diamond‐anvil cell are shown to be reduced substantially when the diamonds diffract at the same setting as the sample – by as much as 50% in some cases. The pressure and wavelength dependence of this process have been studied and also the effect of changing the beam divergence by the use of a synchrotron beam. The consequences for the accuracy of structural information derived from data sets collected at high pressure are considered and a data‐collection strategy for detecting and avoiding the effects of diamond diffraction

ISSN:1600-5767    

DOI:10.1107/S0021889890005635

出版商:International Union of Crystallography    

年代:1990

数据来源: WILEY

摘要:

A single‐crystal study on AlPO4was 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 conventiona

ISSN:1600-5767    

DOI:10.1107/S0021889890005702

出版商:International Union of Crystallography    

年代:1990

数据来源: WILEY

摘要:

Initial tests are described of a high‐resolution small‐angle X‐ray scattering apparatus adapted for operation at high photon energies. The energy chosen was 50 keV, and was limited by the available source. All orders of scattering out to the seventh were observed from a sample of 0.9μm diameter latex spheres in a 4 h experiment. Phase separation in a binary Al–Li alloy was studied by the observation of spherical Al3Li precipitates. This demonstrates that the use of perfect‐crystal collimators and analyzers yields a resolution function which does not depend on photon energy. New sources of high‐energy photons will make such an apparatus invaluable for the study of highly absorbing samples, or samples in difficult environments such as ovens or hig

ISSN:1600-5767    

DOI:10.1107/S0021889890005787

出版商:International Union of Crystallography    

年代:1990

数据来源: WILEY