A Theta-Dependent Error Present in Powder Data of Highly Absorbing Materials: A Surface Roughness Effect?

Masciocchi, N.; Toraya, Hideo; Parrish, William

doi:10.4028/www.scientific.net/msf.79-82.245

Cited by 6 publications

(5 citation statements)

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“…This can reduce the intensity of low-angle re¯ections and lead to anomalously low thermal parameters in re®nement. Corrections have been suggested by Suortti (1972), Masciocchi et al (1991) and Pitschke et al (1993), and have been implemented in some programs.…”

Section: Data Collectionmentioning

confidence: 99%

Rietveld refinement guidelines

et al. 1999

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A set of general guidelines for structure re®nement using the Rietveld (whole-pro®le) method has been formulated by the International Union of Crystallography Commission on Powder Diffraction. The practical rather than the theoretical aspects of each step in a typical Rietveld re®nement are discussed with a view to guiding newcomers in the ®eld. The focus is on X-ray powder diffraction data collected on a laboratory instrument, but features speci®c to data from neutron (both constant-wavelength and time-of-¯ight) and synchrotron radiation sources are also addressed. The topics covered include (i) data collection, (ii) background contribution, (iii) peak-shape function, (iv) re®nement of pro®le parameters, (v) Fourier analysis with powder diffraction data, (vi) re®nement of structural parameters, (vii) use of geometric restraints, (viii) calculation of e.s.d.'s, (ix) interpretation of R values and (x) some common problems and possible solutions.

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Section: Data Collectionmentioning

confidence: 99%

Rietveld refinement guidelines

et al. 1999

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“…It is already known that the microabsorption effect has no or only a minor effect on the lattice constants, the atom positions, and the occupation numbers and that it causes incorrect temperature factors in order to describe the angle-dependent intensity attenuation (Masciocchi et al, 1991;Kumar et al, 1991;Pitschke et al, 1993). However, without correction of microabsorption effect, we approached goodness-of-fit parameters S of 2.89 for sample (1) and 2.41 for sample (2) only.…”

Section: Resultsmentioning

confidence: 99%

Incorporation of microabsorption corrections into Rietveid analysis

1993

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Surface roughness of planar samples causes an additional attenuation of X-ray diffraction intensity measured in Bragg–Brentano geometry. The decrease of intensity becomes stronger with decreasing scattering angle. This is part of the microabsorption effect. Two quantitative expressions describing the microabsorption effect are incorporated into the DBWS 9006-PC Rietveid program [D. B. Wiles and R. A. Young, J. Appl. Crystallogr. 15, 149–151 (1981)]. The procedure is applied to scattering data obtained from YBa2Cu3O7-powder samples with different degree of surface roughness but approximately identical bulk structure. The procedure is proved to work well. However, the values obtained for the parameters of the temperature factors and the microabsorption effect are correlated, and careful discussion is necessary to interpret the results.

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“…Periodic, triangular (Borie, 1981) or rectangular (Masciocchi et al, 1991) modulated 2D surface models allow the direct calculation of the absorption correction by explicitly considering each possible X-ray path through the sample analytically. For more complex models, explicit, analytical treatment of all X-ray paths is not feasible.…”

Section: Introductionmentioning

confidence: 99%

Universal simulation of absorption effects for X-ray diffraction in reflection geometry

Dallmann,

Graetz,

Hock

2024

Acta Cryst Sect A

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Analytical calculations of absorption corrections for X-ray powder diffraction experiments on non-ideal samples with surface roughness, porosity or absorption contrasts from multiple phases require complex mathematical models to represent their material distribution. In a computational approach to this problem, a practicable ray-tracing algorithm is formulated which is capable of simulating angle-dependent absorption corrections in reflection geometry for any given rasterized sample model. Single or multiphase systems with arbitrary surface roughness, porosity and spatial distribution of the phases in any combination can be modeled on a voxel grid by assigning respective values to each voxel. The absorption corrections are calculated by tracing the attenuation of X-rays along their individual paths via a modified shear-warp algorithm. The algorithm is presented in detail and the results of simulated absorption corrections on samples with various surface modulations are discussed in the context of published experimental results.

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A Theta-Dependent Error Present in Powder Data of Highly Absorbing Materials: A Surface Roughness Effect?

Cited by 6 publications

References 0 publications

Rietveld refinement guidelines

Rietveld refinement guidelines

Incorporation of microabsorption corrections into Rietveid analysis

Universal simulation of absorption effects for X-ray diffraction in reflection geometry

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