摘要:

A three‐dimensional dynamic DuMond diagram has been constructed, in which the three axes represent the wavelength and vertical and horizontal divergences of an X‐ray beam. Such a diagram can be used to analyse successive diffraction of multiple crystals. It is simple and clear cut to use this diagram for the analysis and design of crystal collimators, monochromators and spectrometers involving nearly perfect cryst

ISSN:1600-5767    

DOI:10.1107/S0021889888000421

出版商:International Union of Crystallography    

年代:1988

数据来源: WILEY

摘要:

The general principles of single‐ and double‐crystal spectrometers are described using the three‐dimensional DuMond diagram and new formulae for the resolution of the spectrometers are deduced. A method for measuring the fine structure of spectral lines with high precision is suggested and a generalized method of refraction correction is discussed. The CuKα line profile is measured carefully by double‐crystal spectrometers using (nS,nS) and (nV,nR) arrangements, and a hump is found unambiguously on the long‐wavelength side of the

ISSN:1600-5767    

DOI:10.1107/S0021889887011841

出版商:International Union of Crystallography    

年代:1988

数据来源: WILEY

摘要:

A strategy for the determination of crystal structures with large known fragments directly from measured X‐ray powder diffraction intensities is presented. It is based on the automated full‐symmetry Patterson search method described by Rius&Miravitlles [J. Appl. Cryst.(1987).20, 261–269] where the Fourier coefficients of the observed Patterson function are modified to allow the use of powder diffraction intensity data. Its application to two structures, one with simulated and one with experimental data, is

ISSN:1600-5767    

DOI:10.1107/S0021889888000603

出版商:International Union of Crystallography    

年代:1988

数据来源: WILEY

摘要:

An outline and an application of the two‐stage method in neutron powder diffractometry are presented. Stage (1): Individual reflection data like position, half‐width and integrated intensity are analysed by profile fitting. The profile analysis is based on an experimentally determined instrument function and can be applied without prior knowledge of a structural model. A mathematical procedure is described which results in a variance–covariance matrix containing standard deviations and correlations of the refined reflection parameters. Stage (2): The individual reflection data derived from the profile fitting procedure can be used for appropriate purposes either in structure determination or in texture and strain or stress analysis. The integrated intensities are used in the non‐diagonal weighted least‐squares routinePOWLSfor structure refinement. The weight matrix is given by the inverted variance‐covariance matrix of stage (1). This procedure is the basis for reliable and real BraggRvalues and for a realistic estimation of standard deviations of structural parameters. In the case of texture analysis the integrated intensities are compiled into pole figures representing the intensity distribution for all sample orientations of individualhkl. Various examples for the wide application of the two‐stage method in structure and texture analysis are given: structure refinement of a standard quartz specimen, magnetic ordering in the system TbxY1−xAg, preferred orientation effects in deformed marble and texture investigations of a tricli

ISSN:1600-5767    

DOI:10.1107/S0021889888001013

出版商:International Union of Crystallography    

年代:1988

数据来源: WILEY

摘要:

Synchrotron radiation was used to measure the rocking curves from (Ga,In)(As,P) single layers grown on an InP (100) oriented substrate. The incident angle was varied (changing correspondingly the X‐ray incident‐beam wavelength) in order to measure at extremely asymmetrical Bragg diffraction down to a glancing angle of 0.35°. The measured rocking curves could be interpreted by the semi‐kinematic model of Petrashen [Fiz. Tverd. Tela(1974).16, 2168–2175] with corrections for X‐ray refraction and for the width of the rocking curve from the extended dynami

ISSN:1600-5767    

DOI:10.1107/S0021889888001025

出版商:International Union of Crystallography    

年代:1988

数据来源: WILEY

摘要:

The method described in this paper is based on the comparison of distances of lattice planes perpendicular to the surface in a measured sample and in a reference perfect crystal by means of the symmetrical Laue case of X‐ray diffraction. Systematic errors of the method caused by the tilt of the crystals and by the vertical divergence of the incident beam have been analysed thoroughly. From the form of the deformation field in samples cut along the growth axis of an Si ingot it follows that this experimental arrangement is not sensitive to any axial fluctuations of the impurity concentration even if the surface stress relaxation is considered. The method was applied to the investigation of the radial distribution of oxygen atoms in an Si ingot and the presence of a denuded zone near the ingot surface was demonstrate

ISSN:1600-5767    

DOI:10.1107/S0021889888000779

出版商:International Union of Crystallography    

年代:1988

数据来源: WILEY

摘要:

High‐resolution X‐ray diffraction studies of the perfection of state‐of‐the‐art multilayers are presented. Data were obtained using a triple‐axis perfect‐crystal X‐ray diffractometer. Measurements reveal large‐scale figure errors in the substrate. A high‐resolution triple‐axis set up is required, therefore, to obtain structural information about the layers. Measurements of reflectivity from parallel layers are presented as well as measurements of the angular distribution of the layer normal over the illuminated spot. These measurements are supplemented with measurements of scattering obtained in the total exter

ISSN:1600-5767    

DOI:10.1107/S0021889888001177

出版商:International Union of Crystallography    

年代:1988

数据来源: WILEY

摘要:

The optics of successive Bragg reflection by two bent crystals is considered in the lamellar approximation. The optimal curvatures ensuring minimal rocking‐curve widths and good reflection efficiencies are determined. The conditions under which a rocking curve reproduces the reflectivity curve of a bent crystal are indicated. Analytical formulae for the rocking‐curve width and peak intensity are derived for three simple limiting cases. The computations are supported by experimental results obtained with bent perfect silicon cryst

ISSN:1600-5767    

DOI:10.1107/S0021889888001293

出版商:International Union of Crystallography    

年代:1988

数据来源: WILEY

摘要:

Investigations on an MFI/p‐xylene system by time‐resolved X‐ray powder diffraction in two selected angular domains show that it is possible to derive kinetic and diffusion parameters describing a spontaneous desorption process. The corresponding value of the overall diffusion coefficient, calculated for the MFI,8p‐xylene(S)→ MFI,4p‐xylene(S)+ 4p‐xylene(g)reaction, is in the 0.4–0.6 × 10−10cm2s−1range. The desorption proceedsviaa two‐phased system. Accordingly, the only solid species involved in this desorption are the high‐ and low‐coverage XYLII and XYLI phases, containing respectively eight and fourp‐xylene molecules per unit cell. Similar results are also observed for the MFI/benzene, toluene and pyridine systems, which all present high‐coverage phases, with eight molecules per unit cell, d

ISSN:1600-5767    

DOI:10.1107/S0021889888002134

出版商:International Union of Crystallography    

年代:1988

数据来源: WILEY

摘要:

A simple method of mounting a protein crystal on a surface of a plug made from a bundle of parallel milkweed seed fibres has been developed.

ISSN:1600-5767    

DOI:10.1107/S0021889888001463

出版商:International Union of Crystallography    

年代:1988

数据来源: WILEY