Interactions of lattice distortion fields in nano polycrystalline materials revealed by molecular dynamics and X-ray powder diffraction

Leonardi, Alberto; Bish, David L.

doi:10.1016/j.actamat.2017.04.072

Cited by 9 publications

(11 citation statements)

References 80 publications

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“…We characterize the lattice structure distortion for each configuration and the corresponding average over time. 66 The structure coherence is evaluated based on common-neighbor 67 and bond angle 68 analysis, whereas the structure deformation is measured by crystal cell and Voronoi cell deformation 69 methods.…”

Section: Methodsmentioning

confidence: 99%

Particle Shape Control via Etching of Core@Shell Nanocrystals

Leonardi

Engel

2018

ACS Nano

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The application of nanocrystals as heterogeneous catalysts and plasmonic nanoparticles requires fine control of their shape and chemical composition. A promising idea to achieve synergistic effects is to combine two distinct chemical and/or physical functionalities in bimetallic core@shell nanocrystals. Although techniques for the synthesis of single-component nanocrystals with spherical or anisotropic shape are well-established, new methods are sought to tailor multicomponent nanocrystals. Here, we probe etching in a controlled redox environment as a synthesis technique for multicomponent nanocrystals. Our Monte Carlo computer simulations demonstrate the appearance of characteristic non-equilibrium intermediate microstructures that are further thermodynamically tested and analyzed with molecular dynamics. Convex platelet, concave polyhedron, pod, cage, and strutted-cage shapes are obtained at room temperature with fully coherent structure exposing crystallographic facets and chemical elements along distinct particle crystallographic directions. We observe that structural and dynamic properties are markedly modified compared to the untreated compact nanocrystal.

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Section: Methodsmentioning

confidence: 99%

Particle Shape Control via Etching of Core@Shell Nanocrystals

Leonardi

Engel

2018

ACS Nano

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“…Isotropic and anisotropic thermal vibrations, as well as any available microstrain model, translate directly to the properties (e.g. width and skewness) of the peaks' shape in the D-PDF (Leonardi et al, 2013a,c;Leonardi & Bish, 2017;Flor et al, 2019;Scardi et al, 2017). As an example, Gaussian peaks with width proportional to the temperature resemble the harmonic oscillator model expressed by the Debye-Waller factor (Debye, 1912;Waller, 1923).…”

Section: Figurementioning

confidence: 99%

“…The Wilkens model for cubic materials (Wilkens, 1969) and the general model based on the fourth-order invariant introduced by Popa and Adler & Houska (Popa, 1998;Adler & Houska, 1979;Leoni et al, 2007;Martinez-Garcia et al, 2009) both inherently describe the variation of the D-PDF peaks width as a function of dislocation defects' type and density (Leonardi, Leoni, Li et al, 2012;. The model based on the fourthorder invariant can also be used to describe a wide range of microstrain sources, such as surface relaxation and grain boundaries in polycrystalline materials (Scardi et al, 2015;Burgess et al, 2013;Rebuffi et al, 2016;Leonardi & Bish, 2017). Indeed, this model does not generally commit to any specific strain model and is capable of capturing the distortion anisotropy.…”

Section: Figurementioning

confidence: 99%

“…Any information hidden in the diffuse scattering component is ignored in favor of high computing efficiency and statistical significance (Coelho, 2018;Loopstra & Rietveld, 1969;van Laar & Schenk, 2018). The Bragg theory is no longer strictly applicable when dealing with complex disorder scenarios, as well as when the variation of the structure factor across the peaks is significant, because changes in the scattering profile do not conform to such a peak-by-peak treatment (Rebuffi et al, 2016;Leonardi & Bish, 2017).…”

Section: Introductionmentioning

confidence: 99%

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Whole pair distribution function modeling: the bridging of Bragg and Debye scattering theories

Leonardi

2021

IUCrJ

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Microstructure-based design of materials requires an atomic level understanding of the mechanisms underlying structure-dependent properties. Methods for analyzing either the traditional diffraction profile or the pair distribution function (PDF) differ in how the information is accessed and in the approximations usually applied. Any variation of structural and microstructural features over the whole sample affects the Bragg peaks as well as any diffuse scattering. Accuracy of characterization relies, therefore, on the reliability of the analysis methods. Methods based on Bragg's law investigate the diffraction peaks in the intensity plot as distinct pieces of information. This approach reaches a limitation when dealing with disorder scenarios that do not conform to such a peak-by-peak basis. Methods based on the Debye scattering equation (DSE) are, otherwise, well suited to evaluate the scattering from a disordered phase but the structure information is averaged over short-range distances usually accessed by experiments. Moreover, statistical reliability is usually sacrificed to recover some of the computing-efficiency loss compared with traditional line-profile-analysis methods. Here, models based on Bragg's law are used to facilitate the computation of a whole PDF and then model powder-scattering data via the DSE. Models based on Bragg's law allow the efficient solution of the dispersion of a crystal's properties in a powder sample with statistical reliability, and the PDF provides the flexibility of the DSE. The whole PDF is decomposed into the independent directional components, and the number of atom pairs separated by a given distance is statistically estimated using the common-volume functions. This approach overcomes the need for an atomistic model of the material sample and the computation of billions of pair distances. The results of this combined method are in agreement with the explicit solution of the DSE although the computing efficiency is comparable with that of methods based on Bragg's law. Most importantly, the method exploits the strengths and different sensitivities of the Bragg and Debye theories.

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“…Unfortunately, the methods employed by Tsung et al 8 cannot be applied to many systems as nanoparticle syntheses rarely achieve the necessary degree of monodispersity. 9,10 Moreover, scattering techniques like coherent X-ray diffraction are currently limited to nanocrystals roughly 60 nm in diameter. 11 Thus, to better understand strain in core@shell nanoparticles, techniques that provide greater spatial resolution are required.…”

Section: Introductionmentioning

confidence: 99%