Dislocation Effects on the Diffraction Line Profiles from Nanocrystalline Domains

Abstract

A Pd nano-polycrystalline microstructure was simulated by molecular dynamics, including edge or screw dislocations in one of the 50 grains, so as to produce a realistic model of nanocrystalline domain with line defect. The same crystalline domain was also studied, with or without line defects, as a free-standing, isolated nanocrystal. Atomic coordinates of the selected domain were used to generate powder patterns by means of the Debye scattering equation, and these patterns were used as ''experimental'' data to test existing methods of line profile analysis in controlled condition, i.e., with known type and density of defects. Results show that the Krivolgaz-Wilkens theory of dislocation line broadening qualitatively agrees with the MD model, but errors can be larger than 50 pct. A critical issue arises from the instability of the Krivolgaz-Wilkens model when all line profile parameters are simultaneously refined: reasonable results can be obtained by fixing or restricting some parameters.

Combining X‐Ray Whole Powder Pattern Modeling, Rietveld and Pair Distribution Function Analyses as a Novel Bulk Approach to Study Interfaces in Heteronanostructures: Oxidation Front in FeO/Fe3O4 Core/Shell Nanoparticles as a Case Study

“…The plot displays the dependence of the root‐mean‐square displacement (RMSD) versus the distance between two scattering points in the coherent domain. The RMSD is obtained from the root‐mean‐square strain (RMSS) using the relation RMSD = L ·RMSS, where L = n ·λ/2·(sinθ 2 −sinθ 1 ) is the Fourier length (θ 2 −θ 1 is the angular range of the peak profile) . RMSD was chosen instead of RMSS, since one can follow the strain behavior with L .…”

“…This implies that the layers which form the nanocubes are composed by small spheres stacked together (as will be discussed later). The strain analysis was performed using the model proposed by Scardi and Leonardi, where strain anisotropy can be accounted according to the symmetry of the elastic tensor . The model permits calculating the Warren plot, which allows the local atomic displacement to be represented.…”

“…The model permits calculating the Warren plot, which allows the local atomic displacement to be represented. The Warren plot gives the RMSD versus L , where L is the distance between two scattering points inside the coherent domain …”

PVA/NaCl/MgO nanocomposites-microstructural analysis by whole pattern fitting method

“…A multitude of these modelling designs enunciate the significance of line profile analysis [14].These studies embark on use of single-order method for analysis of microstructure [15]. The whole pattern fitting gives us more reliable microstructural parameters compared to other methods [16]. The experimental and simulated x-ray profiles with different weight percentage composition of PVA/NaCl/MgO nanocomposites using whole powder pattern technique is shown in figure 1.…”

100 years of Debye's scattering equation

“…A representative example concerns a test of the validity of the Krivoglaz-Wilkens model (Krivoglaz, 1969;Wilkens, 1970) in the framework of the WPPM approach, generated by constructing a model of a cluster of 50 palladium grains (see Fig. 3) and is reported in Leonardi & Scardi (2015b).…”