Least-squares structure refinement based on profile analysis of powder film intensity data measured on an automatic microdensitometer

Abstract

The Rietveld profile-analysis refinement procedure [Rietveld, J. Appl. Cryst. (1969), 2, 65–71] is here applied to microdensitometer-measured Guinier–Hägg X-ray powder film data (strictly monochromated Cu Kα ₁ radiation). Various functions for describing the profile form of an individual reflection are tested; the most satisfactory fit is obtained for a modified and asymmetrized Lorentz function. The crystal structure of α-Bi ₂O ₃ has been refined and no significant deviations are observed from the results of an earlier single-crystal study [Malmros, Acta Chem. Scand. (1970), 24, 384–396]. An R _F value [roughly comparable with the conventional R( F) value of single-crystal work] of 0.068 was obtained, with standard deviations on the refined positional parameters on average three times larger than those obtained from the single-crystal study. Further examples of the refinement technique are also given which illustrate both its reproducibility and range of application.