scholarly journals New Route to Local Order Models for Disordered Crystalline Materials: Diffuse Scattering and Computational Modeling of Phloroglucinol Dihydrate

2011 ◽  
Vol 11 (6) ◽  
pp. 2045-2049 ◽  
Author(s):  
Lynne H. Thomas ◽  
Gavin A. Craig ◽  
Carole A. Morrison ◽  
Anthony M. Reilly ◽  
Chick C. Wilson
Keyword(s):  
Computational Modeling ◽  
Diffuse Scattering ◽  
Local Order ◽  
Crystalline Materials ◽  
Disordered Crystalline Materials

scholarly journals Nanoscale Order in Molecular Systems from Single Crystal Diffuse Scattering

2014 ◽  
Vol 67 (12) ◽  
pp. 1807 ◽  
Author(s):  
Darren J. Goossens ◽  
T. Richard Welberry
Keyword(s):  
Diffuse Scattering ◽  
Reciprocal Lattice ◽  
Local Order ◽  
Model Structure ◽  
Scattered Intensity ◽  
Great Strength ◽  
Crystalline Materials ◽  
Molecular Systems ◽  
Disordered Structures ◽  
Nanoscale Order

Diffuse scattering – the coherently scattered intensity that is not localised on the reciprocal lattice – contains a wealth of information about the local order (order on the nanoscale) in crystalline materials. Since molecules and atoms will respond most strongly to their local chemical environments, it is a valuable tool in understanding how structure leads to properties. However, at present its collection and analysis are relatively specialised. Monte Carlo (MC) computer simulation of a model structure has become a powerful and well-accepted technique for aiding the interpretation and analysis of diffuse scattering patterns. Its great strength is its flexibility – as long as an MC energy can be defined, a model can be developed and tested. At one extreme a very simplified model may be useful in demonstrating particular qualitative effects, while at the other a quantitative and very detailed description of disordered structures can be obtained. Examples discussed include new results concerning p-chloro-N-(p-chloro-benzylidene)aniline, a molecule showing various degrees of molecular flexibility.

scholarly journals Ultrafast calculation of diffuse scattering from atomistic models

2019 ◽  
Vol 75 (1) ◽  
pp. 14-24 ◽  
Author(s):  
Joseph A. M. Paddison
Keyword(s):  
Diffuse Scattering ◽  
Large Data ◽  
Large Data Sets ◽  
Scattering Data ◽  
Frequency Noise ◽  
Data Sets ◽  
Fast Method ◽  
Crystalline Materials ◽  
Atomistic Models ◽  
Dynamics Simulations

Diffuse scattering is a rich source of information about disorder in crystalline materials, which can be modelled using atomistic techniques such as Monte Carlo and molecular dynamics simulations. Modern X-ray and neutron scattering instruments can rapidly measure large volumes of diffuse-scattering data. Unfortunately, current algorithms for atomistic diffuse-scattering calculations are too slow to model large data sets completely, because the fast Fourier transform (FFT) algorithm has long been considered unsuitable for such calculations [Butler & Welberry (1992). J. Appl. Cryst. 25, 391–399]. Here, a new approach is presented for ultrafast calculation of atomistic diffuse-scattering patterns. It is shown that the FFT can actually be used to perform such calculations rapidly, and that a fast method based on sampling theory can be used to reduce high-frequency noise in the calculations. These algorithms are benchmarked using realistic examples of compositional, magnetic and displacive disorder. They accelerate the calculations by a factor of at least 102, making refinement of atomistic models to large diffuse-scattering volumes practical.

Analysis of diffuse scattering from the mineral mullite

1994 ◽  
Vol 27 (5) ◽  
pp. 742-754 ◽  
Author(s):  
B. D. Butler ◽  
T. R. Welberry
Keyword(s):  
Diffuse Scattering ◽  
Real Space ◽  
Order Parameters ◽  
Scattering Data ◽  
Local Order ◽  
Near Neighbour ◽  
Diffuse Intensity ◽  
Space Model ◽  
Least Squares Techniques ◽  
Space Volume

A full reciprocal-space volume of diffuse scattering data from a single-crystal of the mineral mullite, Al2(Al2 + 2x Si2 − 2x )O10 − x , x = 0.4, was collected. These data were analysed using least-squares techniques by writing an equation for the diffuse scattering that involves only the local order between vacancies on specific oxygen sites in the material. The effect of the large, but predictable, cation shifts on the diffuse intensity is taken account of in the coefficients of the oxygen-vacancy short-range-order intensities. This analysis shows that the vacancies are negatively correlated at the near-neighbour ½ 〈110〉, [110], 〈001〉 and 〈011〉 interatomic vectors and positively correlated along the 〈010〉, 〈101〉, ½ 〈112〉 and ½ 〈310〉 vectors. Subsequent Monte Carlo modelling of the structure based on these local-order parameters demonstrates that the structure of mullite is dominated by effective near-neighbour vacancy–vacancy repulsive interactions. A real-space model of mullite is presented that is approximately consistent with the measured local-order parameters.

scholarly journals Predicting short-range order and correlated phenomena in disordered crystalline materials

2020 ◽  
Vol 6 (35) ◽  
pp. eabc2758 ◽  
Author(s):  
Eric C. O’Quinn ◽  
Kurt E. Sickafus ◽  
Rodney C. Ewing ◽  
Gianguido Baldinozzi ◽  
Joerg C. Neuefeind ◽  
...  
Keyword(s):  
Short Range ◽  
Atomic Scale ◽  
Crystalline Materials ◽  
Radiation Fields ◽  
Straightforward Application ◽  
Structural Distortions ◽  
The Impact ◽  
Disordered Crystalline Materials ◽  
Structural Disordering ◽  
Intense Radiation

Disordered crystalline materials are used in a wide variety of energy-related technologies. Recent results from neutron total scattering experiments have shown that the atomic arrangements of many disordered crystalline materials are not random nor are they represented by the long-range structure observed from diffraction experiments. Despite the importance of disordered materials and the impact of disorder on the expression of physical properties, the underlying fundamental atomic-scale rules of disordering are not currently well understood. Here, we report that heterogeneous disordering (and associated structural distortions) can be understood by the straightforward application of Pauling’s rules (1929). This insight, corroborated by first principles calculations, can be used to predict the short-range, atomic-scale changes that result from structural disordering induced by extreme conditions associated with energy-related applications, such as high temperature, high pressure, and intense radiation fields.

Synchrotron X-ray diffuse scattering from a stable polymorphic material: terephthalic acid, C8H6O4

2017 ◽  
Vol 73 (1) ◽  
pp. 112-121 ◽  
Author(s):  
D. J. Goossens ◽  
E. J. Chan
Keyword(s):  
Phase Transition ◽  
Terephthalic Acid ◽  
Diffuse Scattering ◽  
Structural Phase ◽  
Local Order ◽  
Ambient Conditions ◽  
X Ray Diffraction ◽  
Harmonic Model ◽  
X Ray ◽  
Polymorphic Materials

Terephthalic acid (TPA, C8H6O4) is an industrially important chemical, one that shows polymorphism and disorder. Three polymorphs are known, two triclinic [(I) and (II)] and one monoclinic (III). Of the two triclinic polymorphs, (II) has been shown to be more stable in ambient conditions. This paper presents models of the local order of polymorphs (I) and (II), and compares the single-crystal diffuse scattering (SCDS) computed from the models with that observed from real crystals. TPA shows relatively weak and less-structured diffuse scattering than some other polymorphic materials, but it does appear that the SCDS is less well modelled by a purely harmonic model in polymorph (I) than in polymorph (II), according to the idea that the diffuse scattering is sensitive to anharmonicity that presages a structural phase transition. The work here verifies that displacive correlations are strong along the molecular chains and weak laterally, and that it is not necessary to allow the —COOH groups to librate to successfully model the diffuse scattering – keeping in mind that the data are from X-ray diffraction and not directly sensitive to H atoms.

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