Structural fluctuation evaluation in substances from measurement data

ScienceDaily | 8/21/2018 | Staff
smilingbearsmilingbear (Posted by) Level 4
To realize new functions and performance improvements of functional substances, such as those found in batteries and electronic devices, their structure and structural changes must be evaluated at the atomic-scale. This is because, the structure of the atoms at the nanometer scale dominates their properties. Extended X-Ray Absorption Fine Structure (EXAFS) measurements are widely used to analyze microstructures such as these on an atomic scale.

By performing a Fourier transformation on the measured spectrum of an EXAFS oscillation, microstructure information can be obtained to determine how adjacent atoms are distributed radially. However, the radial distribution obtained by this conventional method is quite different from the actual radial structure. This discrepancy is due to improper expansion with basis functions of vibrating waves having constant amplitude by Fourier transformation, despite the fact that the amplitude of the EXAFS oscillation changes noticeably within the observed range.

Amplitude - Changes - Fluctuations - Variations - Distances

The amplitude changes represent structural fluctuations, which are variations in atomic distances and the mobility of neighboring atoms. These physical properties are indicated by a physical quantity called the Debye-Waller factor. This factor cannot be obtained by Fourier transformation of the EXAFS oscillation because estimating the Debye-Waller factor requires assumptions to be made about a material's microstructure. In other words, since an analysis of the conventional EXAFS oscillation spectrum is based on a hypothetical structure, it is difficult to estimate the Debye-Waller factor unless the material microstructure is previously known.

To solve this problem, researchers focused on the fact that atoms are, in general, regularly distributed, which reflects their chemical structure and bonding states. Furthermore, the distances between atoms (atomic coordinates) are distinct, and can...
(Excerpt) Read more at: ScienceDaily
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