Rietveld refinement of energy-dispersive synchrotron measurements

Abstract

In the past two decades the energy-dispersive diffraction (EDD) method has become a powerful tool in many fields of materials research such as residual stress, texture, and crystal structure analysis, because of its favorable ratio of a comparatively low experimental effort in form of a simple and fixed instrumental setup to a high information content included in the measured diffraction patterns. However, mainly due to the rather poor instrumental resolution only little work has been done so far to apply the well-established methods of diffraction line profile analysis to the EDD data. In the paper, a Rietveld program is introduced that allows for particle size and strain broadening analysis by refining the whole EDD äpattern. With the examples of synchrotron measurements performed on the materials science beamline EDDI at BESSY II on instrumental standard as well as samples exhibiting size and/or strain broadened diffraction lines, it is demonstrated that the generalized Thompson, Cox & Hastings approach (TCH) using pseudo-Voigt functions for describing the diffraction line profiles yields sound and reliable results on the materials microstructure. For a first proof of the theoretical assumptions this Rietveld program is based on, the Pawley approach was used to extract the peak intensities obtained from powder samples affected by microstructural broadening. An excellent agreement with the results of the size-strain round robin was obtained. Future enhancements of the program code which aim at its application to full residual stress and microstructure analysis in the near surface zone and also in the material voläume of polycrystalline materials are discussed.