摘要:

X‐ray, neutron and electron diffraction experiments have revealed the existence of internally ordered Guinier–Preston zones in Al‐(8 to 15 at.%)Mg alloys; diffuse satellites oriented along (100) directions are observed near Bragg peaks and give rise to modulated contrasts by TEM. A small‐angle neutron scattering experiment has been carried out on single crystals and a model is proposed for the interpretation of the observed pattern. The existence of concentration modulations is related to alignments of spherical GP zones along (100) dir

ISSN:1600-5767    

DOI:10.1107/S0021889879012966

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

AγCompton experiment with an annular241Amγ‐source is described. The distribution of the primary intensity in the plane of the sample as well as the scattering angle distribution are evaluated by a Monte Carlo calculation to determine (together with the energy resolution) the total momentum resolution of the experiment. In order to probe the reliability of the experimental arrangement and of the data processing, experimental Compton profiles of water from samples of different thicknesses are compared with the results of an IUCr proj

ISSN:1600-5767    

DOI:10.1107/S0021889879012978

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

The analytical algebraic method developed for the selection of active slip systems in the case of glide on {110} (111) systems [Royer, Mohr&Tavard,J. Appl. Cryst.(1978).11, 35–39] is extended to (111) pencil glide. This approach leads to an algebraic determination of all amounts of glide and corresponding slip plane orientations in both cases of effective slip on three or four systems. Numerical applications have led to a reduction of computer time by a factor of 10−3with respect to previous investigati

ISSN:1600-5767    

DOI:10.1107/S002188987901298X

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

A quasi‐crystalline model has been developed which facilitates calculation of the intensity and radial distribution functions (RDF) for hypothetical molecular arrangements in glasses. Interatomic distances are counted so that each atom in the asymmetric unit `sees' all the other atoms within a given radius of that atom, thus eliminating the edge effects inherent in simply counting all possible interatomic distances between atoms in a finite block of crystal. A disorder parameter is associated with each interatomic distance and incorporates thermal motion and the loss of correlation between atoms with increasing distance due to the non‐periodic nature of amorphous substances. The RDF calculated for the high albite (NaAlSi3O8) structure is in good agreement with the RDF determined experimentally on a polycrystalline sample. Spurious ripples, which are larger than can be explained by termination of the Fourier integral, are observed in the experimental RDF's and suggest a systematic error of 3–5% in the corrected diffraction profile. No single source of error (e.g.scaling, absorption, polarization, background estimation) can account for the observed ripples, but a combination of these sources might result in an error of the magnitude sugg

ISSN:1600-5767    

DOI:10.1107/S0021889879012991

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

X‐ray diffraction methods for determining accurate temperature dependence of lattice constants are discussed; it is suggested that HADOX is best for general use. The accuracy and precision of the method are examined in full detail in terms of sensitivity, resolution and systematic and accidental errors. The examination is mostly given in comparison with the Bond method. An overall accuracy of a lattice‐constant change of one part in 107can be attained, provided due consideration is given to reducing the errors; the main systematic errors limiting the accuracy are those in the temperature of crystals and in the orientation of crystals or crystal holders. To obtain the accuracy mentioned above, the basic suggestions for changes to a prototype apparatus are presen

ISSN:1600-5767    

DOI:10.1107/S0021889879013005

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

A HADOX diffractometer for measuring temperature dependence of lattice constants with a relative accuracy to one part in 107has been designed and constructed. Details of the structure and of the procedures for alignment and measurement are given together with the result of a performance test with silicon crystals. The observed value of the linear expansion coefficient of silicon is (2.72 ± 0.02) × 10−6 K−1at 310 K; this is in good agreement with that previously given by a more accurate thermal expansion experiment and shows the applicability of this

ISSN:1600-5767    

DOI:10.1107/S0021889879013017

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

The symmetrized harmonic method of correcting diffracted X‐ray intensities for preferred orientation in powder samples is applied to tetragonal crystals. According to model calculations the measurement of intensity variation of three or four favourable reflections in a limited range of polar angle (αmaxabout 50 to 60°) makes possible reliable corrections for all reflections, when the distribution of crystallites is regular. After correction for preferred orientation, the residual differences in the test measurements on nickel fluoride and zinc fluoride samples were of the order of ½%, while the largest corrections were 10 to

ISSN:1600-5767    

DOI:10.1107/S0021889879013029

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

The relationshipsh1=h0+Δhnandn=Δh−1(h1−h0) [Gabe (1969). InCrystallographic Computing, edited by F. R. Ahmed. Copenhagen: Munksgaard], establishing the correspondence between the crystal indicesh1and the segment indicesnof a given reflection, can be used to generate the reflections in the unique set, decide whether a reflection belongs to the unique set, find the unique indices of a given reflection and check the correctness of the segment dataΔhandh0. These relationships have been used as the basis of the index generation scheme of the NRC diffractometer program to collect intensity data as a sequence of symmetry‐related sets and as the principle of the ordering algorithm of a data reduction program which can treat all symmetries including the trigonal symmetries in rhombohedral cells without the requirement of any speci

ISSN:1600-5767    

DOI:10.1107/S0021889879013030

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

A double focusing camera for synchrotron radiation is described. Focusing in the vertical plane is achieved with a segmented mirror whereas in the horizontal plane a bent triangular monochromator is used. The entire system is remotely controlled. A few examples of results obtained on biological samples illustrate the performance of the instrument.

ISSN:1600-5767    

DOI:10.1107/S0021889879013042

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

Ten alloys have been investigated in the composition range from V3Si to Cr3Si across the ternary equilibrium diagram using X‐ray diffraction, neutron diffraction, superconducting transition temperature and magnetic susceptibility measurements. Contrary to the results of previous workers it is shown that a two‐phase region is present in the mid‐composition ranges. The vanadium‐rich (VCr)3Si solid solution shows superconducting properties. A magnetic structure appears at low temperatures in certain alloys in the chromium‐rich (CrV)3Si solid solut

ISSN:1600-5767    

DOI:10.1107/S0021889879013054

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY