摘要:

Empirical corrections for the preferred orientation of grains in powder specimens have been generalized. Treatment of asymmetric diffraction geometries [Seemann–Bohlin (Guinier) geometry; glancing‐angle geometry] is included. Inclined textures (in which the maximum of the pole density of preferentially oriented planes is declined from the direction of the diffraction vector) can be also treated. The distribution function of the poles of preferentially oriented planes does not need to be axially symmetric even in the case of inclined textures. Rapid spinning around one axis is needed in this case. The texture‐correction procedure has been implemented in the computer programDBWS‐9006PCfor Rietveld ref

ISSN:1600-5767    

DOI:10.1107/S002188989400960X

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

A practicable and simple averaging procedure of even‐rank tensors is described, realizing an idea of Aleksandrov&Aizenberg [Dokl. Akad. Nauk SSSR, (1967),167, 1028–1031]. It possesses the properties of a geometric mean, identically obeying the physical condition = . The orientation distribution functionf(g) enters the calculations in the form of the well known arithmetic mean. The general case is completed by the consideration of specific (twice‐symmetric) fourth‐rank elastic tensors. Calculations with real and modelled orientation distributions lead to results close to those of much more complicated self‐consisten

ISSN:1600-5767    

DOI:10.1107/S0021889894009623

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

Imperfections in single crystals of the low‐temperature form of barium boric oxide grown by the flux method were observed and studied by X‐ray diffraction topography. The main structural defects are dislocations with severe pinning at both ends and impurity decoration, impurities, helical dislocations, dislocation loops, inclusions, electric domains, crystal boundariesetc. The possible origins of defects together with their contrast are discussed briefly from the structural point of v

ISSN:1600-5767    

DOI:10.1107/S0021889894011027

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

Calculations of powder diffraction peaks using a model of tiny (diameter a few nm) spherical crystals log normally distributed in size with and without surface relaxation are presented. The calculated peak shapes are more nearly Gaussian than Cauchy (Lorentzian). Surface relaxation can produce small variations in peak positions, order‐dependent peak widths and asymmetric tails. The latter may be quite pronounced in the smaller particles and are qualitatively similar to recent data taken on nanometre‐sized crystals. This suggests that comparison of model calculations with X‐ray powder data of single peaks or, preferably, entire diffraction patterns (perhaps as part of a Rietveld refinement) may allow probing of surface atom positions in nanometre‐sized pa

ISSN:1600-5767    

DOI:10.1107/S0021889894011039

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

Numerical image treatment has been used for the enhancement and the analysis of synchrotron white‐beam topographs. Images are recorded either during the experiment by means of an X‐ray‐sensitive camera or after the experiment from photographic films. Filters are designed to avoid artefacts such as the Gibbs effect. Filtering has been applied to the study of the propagation of surface acoustic waves in piezoelectric materials and ferromagnetic domains in Fe–Si crystals, illustrating the interest of Fourier filtering for a deep analysis of X‐ray t

ISSN:1600-5767    

DOI:10.1107/S0021889894011076

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

The problem of the distribution of the misorientation angle for symmetric randomly oriented objects is solved. It concerns, in particular, the crystallites in polycrystalline materials. The solution is the reference point for materials with nonrandom orientation distribution of crystallites and no correlations between the orientations of the neighbouring grains. The method applied is based on Rodrigues parametrization of rotations. The results for all point‐symmetry groups are give

ISSN:1600-5767    

DOI:10.1107/S0021889894011088

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

Imperfections in the (100), (010) and (001) plates of an inorganic nonlinear crystal of lithium boric oxide [lithium triboron (III) tetraoxide] (LiB3O5), prepared from different blocks, have been studied by means of X‐ray projection topography. The experimental results show that there are mainly grown‐in dislocations withb= [100], [101], [10], [001]and [011], glide dislocations in the system of (010)[101], inclusion‐induced dislocations almost all withb= [101], [10]and [001], distributed in a network parallel to the (010) plane, inclusions with the orthorhombic configuration and a long stripe to which there is only one gas bubble attached, and assigned to be the negative crystals. All dislocations run nearly straight and are of the pure screw type. The origins of defect formation and some other crystal properties are discussed in terms of the stru

ISSN:1600-5767    

DOI:10.1107/S002188989401112X

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

The conditions for appearance of the isoscattering points of one‐ and two‐dimensional systems have been theoretically derived using the ideal models of oriented membranes and fibers. The positions* of the isoscattering point of a one‐dimensional system is given bys* =n/(2R0), wherenis a positive integer and 2R0is the thickness of the membrane. For a two‐dimensional system, the positions* is given byJ1(2πs*R0) = 0, whereJ1is the first‐order Bessel function andR0is the radius of

ISSN:1600-5767    

DOI:10.1107/S0021889894012197

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

Thermal expansion of caesium halides has been approximated by a quasiharmonic approach (QHM) [Reeber (1975).Phys. Status Solidi A,32, 321–331; Reeber&Haas (1984).Thermal Expansion, Vol. 8, pp. 31–48] and predicted at high temperature with a modified quasiharmonic model (MQHM) [Wang&Reeber (1995).J. Phys. Chem. Solids, in the press]. Formation enthalpies of high‐temperature defects have also been obtained by fitting lattice differences between a real and an approximate perfect crystal (QHM). Typical values of the coefficients of thermal expansion and lattice parameters are

ISSN:1600-5767    

DOI:10.1107/S0021889894014895

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY

摘要:

This paper describes a novel duMond‐configuration monochromator for high‐resolution X‐ray diffraction. The device consists of two single‐crystal blocks of silicon each containing two beam channels cut respectively parallel to and 17.65° from the (011) planes. In the high‐intensity mode, with CuKα1, radiation, the beam divergence is 11.5" and the dispersion is 1.3 × 10−4with intensity comparable with that from a symmetric Ge 022 device. The high‐resolution setting has a divergence of 4.4" and dispersion of 4.9 × 10−5, the intensity being a factor of ten lower than in the high‐intensity setting. Parallel lateral translation of the two elements permits a rapid switch between the high‐resolution and

ISSN:1600-5767    

DOI:10.1107/S0021889895000355

出版商:International Union of Crystallography    

年代:1995

数据来源: WILEY