Crystal structure analysis from powder diffraction data

Abstract

Careful experimental techniques, especially with synchrotron radiation, give well-resolved diffraction patterns. Remaining overlapping peaks can be separated by profile analysis and profile fitting. The mathematical formalism is given. The derived parameters are: peak positions for lattice constants, integrated intensities for crystal structure work and half-width for line broadening analysis. Crystal structure refinements with the powder least-squares program POWLS yield R factors routinely around R = 1.5% and as low as R = 0.6%. For actual structure analysis Fourier maps have been calculated in the case of the orthorhombic olivine analogue Mg 2 GeO 4 . Another non-trivial example concerns CeO 2 , where chemical bonding features are derived. From an analysis of anomalous dispersion in Yb 2 O 3 the correction terms f ′ have been derived as a function of energy for four wavelengths measured close to the L-absorption edge of Yb.