Fundamental parameters approach in the Rietveld method: a study of the stability of results versus the accuracy of the instrumental profile

The Rietveld refinement method is a valuable tool for structural and microstructural analysis of a variety of crystalline materials. In spite of many important developments in the last decade, most current Rietveld programs suffer from a number of drawbacks. In order to overcome these disadvantages, the “fundamental parameter approach” (FPA) has been used recently. The FPA uses a convolution-based method to build up X-ray line profiles. Instrumental and sample aberrations are calculated from first principles, and convoluted with the emission profile to form the final line profile. Although this methodology eliminates the need for a standard, in practice some instrumental parameters must be refined, resulting in certain empiricism in this procedure. Therefore, the comparison with a strain-free and ‘infinite crystallite size’ standard becomes necessary. In this work we have performed a study of the stability of quantitative analysis and microstructural results versus simulated inaccurate instrumental profiles. All the FPA calculations were performed on X-ray diffraction data from a technologically attractive and scientifically challenging system: liquid-phase-sintered SiC (LPS SiC).