International Union of Crystallography Commission on Crystallographic Apparatus. Accuracy of structure factors from X-ray powder intensity measurements

Abstract

The accuracy of the determination of the structure factors from a powder diffraction measurement is studied in light of a representative example: nickel with Cu Kct radiation. Various sources of error in the absolute measurement and methods of sample characterization are discussed. The contributions of various extraneous scattering mechanisms are assessed. From these considerations it is possible to separate the Bragg scattering, providing measurements are made through virtually the entire angular range. Results are given in detail for a standard sample, a duplicate of which can be made available to interested workers. The relationship of these results to the structure factors of the sample is discussed in terms of a model calculation, in terms of line shape analysis, and in terms of some comparative measurements on various samples of Ni and MgO. All these analyses indicate the impossibility of preparing a single sample which is ideally mosaic. Thus it is incorrect to relate the measured integrated reflection to the structure factor with the customary simple formula when high accuracy is required.

Compton scattering experiments with monochromatic W Kα1 radiation

“…(2 ~_ 10 -4. The flux is estimated from the integrated intensities of reflections from a standard powder sample (Suortti & Jennings, 1977) and the result nmo,o ~-10 v photons s-1 agrees well with the theoretical value. The energy spectrum of the beam was measured with an intrinsic Ge detector.…”

X-ray Rietveld refinement using Debye–Scherrer geometry

“…These aberrations, which are well known for all diffraction geometries (see e.g. Wilson, 1963;Suortti & Jennings, 1971;Suortti, 1972;Langford & Wilson, 1973;Wilson, 1973;Suortti, 1977;Ersson, 1979;Scott, 1981), have not previously been included in X-ray Rietveld refinement, an omission which we believe is largely responsible for the method's limited success to date. The results of the present work suggest that a similar formulation for the Bragg-Brentano and Guinier geometries is desirable, although in these cases, which are more sensitive to misalignment of the apparatus, greater mathematical complexity would probably be required.…”

An X-ray determination of the thermal expansion of silver and copper-base alloys at higher temperatures. III. Ag–Ge and Cu–Ge

“…Although not counted in the PHA window set for the characteristic radiation they increase drastically the dead time of the counting sequence, as demonstrated by Suortti & Jennings (1977).…”