ISSN:1600-5767    

DOI:10.1107/S0021889895099699

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

The possibilities for monitoring phase transitions in single crystals using limited sections of data are considered. Specifically, the novel technique of monitoring phase transitions using a single three‐dimensional data frame measured by the time‐of‐flight Laue technique has been investigated using simulations. These have shown there is real potential in this technique, allowing `dynamic' measurements of single‐crystal materials. The time‐of‐flight Laue technique is shown to be of particular utility in this area and the possibilities for single‐shot monitoring of phase transitions are assessed, evaluated

ISSN:1600-5767    

DOI:10.1107/S002188989400467X

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

Even with well aligned modern diffractometers, the wide‐range diffraction patterns of diffusely scattering materials are distorted owing to factors associated with finite specimen length, strong Compton scattering, high X‐ray transparency causing asymmetric broadening and displacement of interference maxima towards smaller angles, and possibly small‐angle scattering. The small‐angle scattering can extend far enough to overlap the first interference maximum and the peak displacement can lead to significantd‐spacing errors. Simple methods of correcting for these distortions are presented. These corrections are especially important in situations where overlapping peaks ar

ISSN:1600-5767    

DOI:10.1107/S0021889894006333

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

This work is devoted to a new generation of cold‐neutron interferometers based on bidimensional diffraction. The use of multilayer coatings in the classical Ioffe difffraction‐grating neutron interferometer is proposed. This interferometer combines the properties of two periodic structures, namely the dispersion by a diffraction grating and the high reflectivity ensured by the multilayer coating. All the cold‐neutron interferometer devices (two diffraction gratings and two mirrors) must be multilayered with Ni–Ti or Fe–Ge for unpolarized or polarized neutron interferometry experiments, respectively. The computed results, giving the characteristics of the multilayer‐coated amplitude diffraction grating are discussed within a kinematic model. An Ni–Ti multilayered amplitude diffraction grating for use at λ = 5 Å is presen

ISSN:1600-5767    

DOI:10.1107/S0021889894007788

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

A differential scanning calorimeter with a temperature range of 77 to 873 K has been developed for use in combination with either time‐resolved X‐ray scattering or high‐resolution energy‐dispersive powder diffraction studies using synchrotron radiation. The first results of successful experiments are briefly

ISSN:1600-5767    

DOI:10.1107/S0021889894008320

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

The staging phase transitions during deintercalation of CuCl2‐intercalated graphite have been studied using real‐time X‐ray powder diffraction. The evolution of the diffraction pattern observed during the deintercalation revealed gradual changes in phase composition. A detailed profile analysis enabled a quantitative phase analysis and visualized the phase composition at any time during the reaction. Conclusions concerning the mechanism and kinetics of deintercalation are compared with theoretical re

ISSN:1600-5767    

DOI:10.1107/S0021889894007776

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

X‐ray small‐ and medium‐angle scattering of partially ordered or semicrystalline materials is composed of background scattering from the form scattering of the components and from the amorphous phase and of peaks from the scattering of the crystallites. By the slit geometry of X‐ray diffractometers constructed for registration of small‐ and medium‐angle X‐ray scattering, the diffuse scattering and the peaks are distorted and the peak positions and half‐widths are changed. A program module based on the Akima interpolation [Akima (1970).J. Assoc. Comput. Math.17, 589–602] is proposed for calculation of the first derivative of the complete smeared scattering curve, which is then explicitly used in direct collimation correction procedures. The desmearing of scattering curves from semicrystalline starch samples proves the convenience of the method for low‐noise conditions and exhibits a significant gain of measuring time in comparison with data of comparable accuracy but measured with Soller‐slit collimation systems or desmeared with direct methods usin

ISSN:1600-5767    

DOI:10.1107/S0021889894008319

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

Successful integration of the spot intensities on a single‐crystal X‐ray diffraction image depends on the ability to predict the spot positions accurately throughout the image. In some image‐plate systems, there are spatial distortions, resulting from imperfections in the scanning system, for which corrections need to be made before a satisfactory match between observed and predicted spot positions can be achieved. A procedure to correct for this spatial distortion as part of the refinement procedure used in processing Laue diffraction data is described. The spatial distortion is modelled using polynomial functions. For the test and other images considered, with a pixel size of 88 μm, the root‐mean‐square (r.m.s.) deviations between the observed and predicted spot positions were reduced from up to 1.4 pixels to 0.4 pixels or less for the 400 or so spots used in the refinements and good predictions throughout the images

ISSN:1600-5767    

DOI:10.1107/S0021889894008824

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

The form of the transmission factor for sample geometries encountered in X‐ray and neutron fibre diffraction studies is considered. Transmission factors obtained by Monte Carlo experiments and a simple first‐order approximation are compared and agree to within 1% for studies of the distribution of water and cations around DNA. The first‐order approximation has the advantage of being simple and less computationally expe

ISSN:1600-5767    

DOI:10.1107/S0021889894009635

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

TheXABS2 Fortran program calculates an empirical absorption correction based on minimization of the 2 differences betweenF2obsandF2calc. The basic algorithm has been used in the crystallography laboratory at the University of California, Davis for over a decade, in the form of the programXABS. XABSrelied upon an approximately linear relationship for spherical crystals between the transmission factor and sin2θforθ≃ 30° whenμR≃ 5. InXABS2, deviations from linearity are accounted for by a cubic equation in sin2θ, which makes it applicable over the whole range of diffraction angle. The program needs no data in addition to the unique set but assumes a bisecting (symmetric) data‐collection mode on a four‐circle diffractometer. Since it does not require knowledge of the diffractometer setting angles, it can be applied even in cases where details of the original data collection

ISSN:1600-5767    

DOI:10.1107/S0021889894009428

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY