Whole diffraction pattern-fitting of polycrystalline fcc materials based on microstructure

Abstract:

A method is proposed for modelling the complete diffraction pattern of fcc polycrystalline materials. The algorithm permits a simultaneous refinement of several parameters related to microstructure and lattice defects responsible for line broadening effects. Linear (dislocations) and planar (stacking faults) defects are considered in detail, together with the effect of size and shape of coherent scattering domains (crystallites). Experimentally observed profiles are modelled by Voigt functions, whose parameters are connected with those describing the dislocation field (dislocation density, outer cut-off radius, average contrast factor), twin and deformation fault probabilities, and domain size, also considering the effect of a symmetrical instrumental profile. Domain shape is assumed spherical, with a lognormal distribution of diameters; however, the approach can be generalised to different shapes and size distributions. The proposed algorithm can be extended to other crystalline structures, and can be used within the Rietveld method or as a Whole Powder Pattern Fitting (WPPF), as in the present work.