Advanced approach to the local structure reconstruction and theory validation on the example of the W L₃-edge extended x-ray absorption fine structure of tungsten

Abstract

Abstract. Atomistic simulations of the experimental W L 3 -edge extended X-ray absorption fine structure (EXAFS) of bcc tungsten at T = 300 K were performed using classical molecular dynamics (MD) and reverse Monte Carlo (RMC) methods. The MD-EXAFS method based on the results of MD simulations allowed us to access the structural information, encoded in EXAFS, beyond the first coordination shell and to validate the accuracy of two interaction potential models -the embedded atom model potential and the second nearest-neighbor modified embedded atom method potential. The RMC-EXAFS method was used for more elaborate analysis of the EXAFS data giving access to thermal disorder effects. The results of both methods suggest that the correlation in atomic motion in bcc tungsten becomes negligible above 8Å. This fact allowed us to use the EXAFS data to determine not only mean-square relative displacements of atomic W-W pair motion but also mean-square displacements of individual tungsten atoms, which are usually accessible from diffraction data only.

Local structure of A-atom in ABO3 perovskites studies by RMC-EXAFS

“…At the same time, the distribution of the nearest neighbors Ba-O distances for all temperatures is noticeably wider than that for Ba-Ti as second nearest neighbor, despite that a spread of the Ba-Ti distances for equilibrium positions (1×3.370 Å, 3×3.430 Å, 3×3.501 Å and 1×3.583 Å at 40 K) is comparable to that for Ba-O (3×2.786 Å, 6×2.828 Å and 3×2.886 Å at 40 K). Usually it is expected that RDF becomes wider for further coordination shells as a correlation diminishes with increasing of the distance Jonane et al (2018). So, it is a very clear indicator that we have observed a pronounced Ba-Ti correlation in the second coordination shell of Ba.…”

Neural Network Approach for Characterizing Structural Transformations by X-Ray Absorption Fine Structure Spectroscopy

“…Knowing the atomic trajectories in MD simulations, we calculate the corresponding RDFs, as well as the corresponding time-and ensemble-averaged EXAFS (MD-EXAFS). As we have demonstrated before [46,[51][52][53], MD allows one to generate EXAFS spectra in a qualitative agreement with experimental data. A very accurate agreement between MD-EXAFS and experimental EXAFS is not required here, since MD-EXAFS data are used solely for the purpose of establishing the relation between EXAFS and RDF features, and not for direct matching with ex-…”

Treatment of disorder effects in X-ray absorption spectra beyond the conventional approach

“…4 (lower panel)). The obtained mean square displacements (MSD) σ 2 W are in agreement with previously reported experimental and theoretical results (Jonane et al (2018a)).…”

“…MFP. Examples for bulk and nanocrystalline nickel oxide(Anspoks et al (2012)) and body-centred-cubic (bcc) tungsten(Jonane et al (2018a)) are shown inFig. 1.…”