The Experts below are selected from a list of 27471 Experts worldwide ranked by ideXlab platform
Walter Steurer - One of the best experts on this subject based on the ideXlab platform.
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yell a computer program for diffuse scattering analysis via three dimensional delta pair distribution function refinement
Journal of Applied Crystallography, 2014Co-Authors: Arkadiy Simonov, Thomas Weber, Walter SteurerAbstract:Yell, a program for routine refinement of disorder models against single-Crystal diffuse scattering data, is presented. The analysis is based on the three-dimensional delta pair distribution function (3D-ΔPDF) method, which provides direct access to interatomic correlations in Real Crystal structures. Substitutional, displacive and size-effect disorder models are covered. The input file format supports flexible usage of arithmetic expressions for constraining dependent parameter values. The program is designed to be run on desktop computers. By using an efficient fast-Fourier-transform-based diffuse scattering calculation algorithm, full least-square refinements of medium complexity disorder models may be performed within minutes or hours, even if the experimental diffuse scattering is represented by large and fine-sampled reciprocal space volumes. The program is written in C++ and the source code is distributed under the GPL licence. Binary distributions are currently available for Mac and Windows operating systems.
Arkadiy Simonov - One of the best experts on this subject based on the ideXlab platform.
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yell a computer program for diffuse scattering analysis via three dimensional delta pair distribution function refinement
Journal of Applied Crystallography, 2014Co-Authors: Arkadiy Simonov, Thomas Weber, Walter SteurerAbstract:Yell, a program for routine refinement of disorder models against single-Crystal diffuse scattering data, is presented. The analysis is based on the three-dimensional delta pair distribution function (3D-ΔPDF) method, which provides direct access to interatomic correlations in Real Crystal structures. Substitutional, displacive and size-effect disorder models are covered. The input file format supports flexible usage of arithmetic expressions for constraining dependent parameter values. The program is designed to be run on desktop computers. By using an efficient fast-Fourier-transform-based diffuse scattering calculation algorithm, full least-square refinements of medium complexity disorder models may be performed within minutes or hours, even if the experimental diffuse scattering is represented by large and fine-sampled reciprocal space volumes. The program is written in C++ and the source code is distributed under the GPL licence. Binary distributions are currently available for Mac and Windows operating systems.
Philippe Thomas - One of the best experts on this subject based on the ideXlab platform.
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Origin of the strong optical nonlinearity of tellurium oxide–based compounds: The specific case of BaTe2O6
Journal of Alloys and Compounds, 2016Co-Authors: David Hamani, Antoine Plat, Maggy Colas, Julie Cornette, Olivier Masson, Philippe ThomasAbstract:This paper is a contribution to the understanding of the Crystal chemistry origin of the strong nonlinear optical properties of tellurium oxide-based compounds. The particular case of the BaTe2O6 (BaTeIVTeVIO6) phase has been investigated. The structure refinement using single Crystal X-ray diffraction confirms that the TeIV atom is located in an unclassical TeO5 environment with one exceptionally short Te-O bond (1.82 Å) and four long ones (2.12 Å). The vibrational analysis points out that in this environment, from the spectrochemical point of view, the short bond is at the origin of a quasi-isolated TeIVO2+ molecular ion whereas the four longer bonds traduce weak interactions. Relationships have been established between the TeIV-O bond lengths and the khi(3) susceptibility. The four long bonds, belonging practically to the xz-plane and involving the TeIV d-orbitals contribution, are at the origin of the high khi(3) xxxx and khi(3) zzzz values (30.0 and 44.3x10-13 esu respectively). The short Te- O bond, directed along the y-direction, is responsible for the lower khi(3) yyyy value (3.2x10-13 esu). This study is the first obvious confirmation for a Real Crystal lattice of the high superiority of the nonlinear polarizability of the weak intermolecular Te-O bonds over that of the strong molecular Te-O ones.
Thomas Weber - One of the best experts on this subject based on the ideXlab platform.
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yell a computer program for diffuse scattering analysis via three dimensional delta pair distribution function refinement
Journal of Applied Crystallography, 2014Co-Authors: Arkadiy Simonov, Thomas Weber, Walter SteurerAbstract:Yell, a program for routine refinement of disorder models against single-Crystal diffuse scattering data, is presented. The analysis is based on the three-dimensional delta pair distribution function (3D-ΔPDF) method, which provides direct access to interatomic correlations in Real Crystal structures. Substitutional, displacive and size-effect disorder models are covered. The input file format supports flexible usage of arithmetic expressions for constraining dependent parameter values. The program is designed to be run on desktop computers. By using an efficient fast-Fourier-transform-based diffuse scattering calculation algorithm, full least-square refinements of medium complexity disorder models may be performed within minutes or hours, even if the experimental diffuse scattering is represented by large and fine-sampled reciprocal space volumes. The program is written in C++ and the source code is distributed under the GPL licence. Binary distributions are currently available for Mac and Windows operating systems.
D M Barnett - One of the best experts on this subject based on the ideXlab platform.
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motion and rotation of small glissile dislocation loops in stress fields
Physical Review Letters, 2004Co-Authors: W G Wolfer, T Okita, D M BarnettAbstract:Atomistic computer simulations of small clusters of self-interstitials have revealed that these clusters are highly mobile along certain Crystallographic directions. Their thermal mobility and Brownian motion along these directions rapidly decreases, however, as the size of the cluster increases. A review of these computer simulations has been provided by Osetsky et al. [1], and more recent studies are given by Marian et al. [2]. All these studies have shown that the activation energy for cluster diffusion reaches a saturation value, while the pre-exponential factor continues to decline with the cluster or loop size. The diffusion of loops containing more than one hundred interstitials becomes too slow to be quantified with molecular dynamics simulations. Nevertheless, since the activation energy for migration becomes nearly independent of the loop size, they remain very mobile if forces act on them, even though their Brownian motion becomes insignificant. Such forces naturally exist in Real Crystal due to internal stress fields originating from other defects, in particular from dislocations. Small clusters of self-interstitials, when no longer subject to rapid Brownian migration, are of course synonymous with small prismatic dislocation loops. When their Burgers vectors are aligned along one of the possible glide directions, they can move on one-dimensional trajectories in response to the force exerted by their elastic interaction with stress fields of other defects. As we shall see, this force depends among other factors on the orientation of the dislocation loop, and in turn, the orientation is affected by the stress field. In other words, the motion of a small prismatic dislocation loop on its glide prism has three degrees of freedom, namely its position along the glide prism, and the orientation of its normal vector (normal on the loop plane) in relation to its Burgers vector or glide direction. The specification of the latter requires then two angles, hence a total of three degrees of freedom for one-dimensional motion. Kroupa [3] has long ago pointed out that stress fields exert both a net force and a net torque on small dislocation loops that he derived from the Peach-Koehler force. Numerical studies of both force and torque have been carried out by Ghoniem et al.[4] for small prismatic dislocation loops interacting with a near-by dislocation, assuming however, a fixed orientation of the loop normal vector.
