Incorporation of microabsorption corrections into Rietveid analysis

Abstract

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.

Synthesis, Structural Characterization, and Physical Properties of the New Transition Metal Oxyselenide Ce2O2ZnSe2

“…[17][18][19] A combined X-ray and neutron (6 detector banks) refinement was carried out using room-temperature scans. The background (shifted Chebychev), sample height (DIFA/DIFC/ZERO for neutron refinements), peak profiles, a March Dollase unidirectional preferred orientation correction 20 along 001 (X-ray only), a Pitschke surface roughness correction, 21 lattice parameters, atomic positions, isotropic thermal parameters, absorption correction, and a phase fraction of the Ce 2 O 2 Se impurity phase (~5 wt%) were refined. Selected area electron diffraction (SAED) data were collected using a Jeol 2100F transmission electron microscope operating at 200 keV.…”

Rietveld refinement guidelines

“…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.…”

Microabsorption of scattered X-rays and its dependence on incidence angle in the nonsymmetric reflection case

“…It is plausible that for /3 = 3 ° the absorption behaviour deviates qualitatively from that for/3 > 6 °, since for/3 = 3 ° the X-ray beam penetrates only a surface layer, the thickness (sin/3/%~o) ~-0.6 pm of which is of the order of and Pitschke et al (1992) for samples of the powder material used here. Fig.…”

“…Equation (2) is inserted into The special case (i) of vanishing surface roughness follows for t o = 0. Using the value to = 1.06 I.tm estimated for sample (i) by means of an X-ray absorption analysis with BraggBrentano geometry Pitschke et al, 1992) and the parameters s o = 0.52 and Po = 1.65 x l0 s m-1, one obtains the theoretical curves plotted in Fig. 4(b).…”