Dataset Information

X-ray Scattering and O-O Pair-Distribution Functions of Amorphous Ices.

ABSTRACT: The structure factor and oxygen-oxygen pair-distribution functions of amorphous ices at liquid nitrogen temperature ( T = 77 K) have been derived from wide-angle X-ray scattering (WAXS) up to interatomic distances of r = 23 Å, where local structure differences between the amorphous ices can be seen for the entire range. The distances to the first coordination shell for low-, high-, and very-high-density amorphous ice (LDA, HDA, VHDA) were determined to be 2.75, 2.78, and 2.80 Å, respectively, with high accuracy due to measurements up to a large momentum transfer of 23 Å^-1. Similarities in pair-distribution functions between LDA and supercooled water at 254.1 K, HDA and liquid water at 365.9 K, and VHDA and high-pressure liquid water were found up to around 8 Å, but beyond that at longer distances, the similarities were lost. In addition, the structure of the high-density amorphous ices was compared to high-pressure crystalline ices IV, IX , and XII, and conclusions were drawn about the local ordering.

SUBMITTER: Mariedahl D

PROVIDER: S-EPMC6095636 | biostudies-literature | 2018 Aug

REPOSITORIES: biostudies-literature

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X-ray Scattering and O-O Pair-Distribution Functions of Amorphous Ices.

Mariedahl Daniel D Perakis Fivos F Späh Alexander A Pathak Harshad H Kim Kyung Hwan KH Camisasca Gaia G Schlesinger Daniel D Benmore Chris C Pettersson Lars Gunnar Moody LGM Nilsson Anders A Amann-Winkel Katrin K

The journal of physical chemistry. B 20180723 30

The structure factor and oxygen-oxygen pair-distribution functions of amorphous ices at liquid nitrogen temperature ( T = 77 K) have been derived from wide-angle X-ray scattering (WAXS) up to interatomic distances of r = 23 Å, where local structure differences between the amorphous ices can be seen for the entire range. The distances to the first coordination shell for low-, high-, and very-high-density amorphous ice (LDA, HDA, VHDA) were determined to be 2.75, 2.78, and 2.80 Å, respectively, wi ...[more]

PMID: 30036063

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Project description: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.

Dataset Information

X-ray Scattering and O-O Pair-Distribution Functions of Amorphous Ices.

Publications

X-ray Scattering and O-O Pair-Distribution Functions of Amorphous Ices.

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