Profile analysis of X-ray powder diffraction data.

Abstract

Various strategies have been tested for obtaining integrated intensities from x-ray powder diffractometer data. An asymmetric pseudo-Voigt profile function was used to fit the pattern in the region above 2θ = 35̊ (Cu-Kα radiation). At lower angles where the asymmetry was strongest and the profile function not suitable the peaks were integrated numerically. A smooth background function was estimated from the regions of minimum intensity of the pattern. The profile parameters were initially refined in small ranges of about 10̊ 2θ in order to determine their 2θ-dependence. Thereafter final refinements of peak intensities were undertaken using the profile parameters thus determined. Analysis of data from the mineral Fe-akermanite, Ca₂Mg₀. ₄Fe₀. δSi₂O₇, generated 173 integrated intensities with 1 > 2δ(1) out of 187 positions separated in 2θ by more than 0,02̊. Of the total of 213 reflections in the range, those overlapping exactly or separated by < 0,02̊ were treated as single peaks. The structure was refined using an overall isotropic temperature parameter and a parameter to compensate for preferred orientation, giving an unweighted residual of 10,4% for 14 parameters.