Whole Powder Pattern Modelling for the study of nanocrystalline and imperfect materials

Paolo Scardi & Matteo Leoni

Department of Materials Engineering and Industrial Technologies, University of Trento,

38050 via Mesiano 77, Trento ITALY

e-mail: Paolo.Scardi@unitn.it

The growing interest in nanostructured materials and devices has given new impetus to the research on diffraction Line Profile Analysis (LPA). Concurrently, the research on powder diffraction techniques moved toward an increasing integration of methods, in the attempt at providing structural and microstructural information from a single, combined refinement procedure.

The Whole Powder Pattern Modelling (WPPM) approach was devised according to the philosophy of analysing powder diffraction data on the base of physical models of the real microstructure, without using a priori fixed analytical peak-profile functions. Main models consider the effect of (i) crystalline grain shape and size distribution, (ii) line defects (dislocations), (iii) structural mistakes (e.g., planar defects like twin and deformation faults or anti-phase domain boundaries) and (iv) grain surface-relaxation effects, but in principle any possible source of line profile effects can be easily included in the general WPPM algorithm.

The present work addresses recent developments in the WPPM approach. Besides reviewing the basic theory underlying the WPPM, refinement results for nanocrystalline and heavily deformed materials are shown and discussed in comparison with the outcome of traditional line profile analysis methods. Actual limits and future prospects in LPA are also discussed.