Speaker
Description
Tungsten(VI) oxide (WO$_{3}$) is widely studied for photochromic and solar-energy-related applications, where its functional properties are strongly connected with changes in electronic structure and local atomic arrangement [1]. In nanocrystalline WO$_{3}$, the local structure can be sensitive not only to chemical modification, such as protonation, but also to synchrotron X-ray exposure during characterization. Therefore, understanding beam-induced structural changes is important for the correct interpretation of X-ray absorption spectroscopy data.
WO3 nanoparticles were synthesized using a modified polyol process [2]. X-ray diffraction measurements indicated an average crystallite size of 3-5 nm. Part of the sample was additionally protonated through hydrogen spillover on metallic indium in an acidic environment, resulting in HₓWO₃ nanoparticles. X-ray absorption spectroscopy at the W L$_{3}$-edge was performed at 300 K at the DESY PETRA III P64 beamline in Hamburg, Germany [3]. EXAFS spectra were collected for both as-prepared WO3 and protonated HxWO3 nanoparticles during exposure to the synchrotron X-ray beam.
The EXAFS spectra were analyzed using the reverse Monte Carlo method combined with an evolutionary algorithm [4]. This approach allowed the reconstruction of three-dimensional atomic configurations consistent with the experimental spectra and enabled detailed analysis of W-O and W-W radial distribution functions, as well as W-O-W bond-angle distribution functions.
The RMC-EXAFS results reveal beam-induced changes in the local structure of both as-prepared and protonated WO₃ nanoparticles. The effect is more pronounced for the protonated HₓWO₃ sample, where changes in the W-O and W-W radial distribution functions and in the W-O-W angular distribution indicate partial bleaching, corresponding to a structural evolution back toward the initial WO$_{3}$-like state. In the as-prepared WO$_{3}$ nanoparticles, the observed changes are smaller and may be related to the formation or rearrangement of W$^{5+}$ color centers under X-ray exposure. These results demonstrate that synchrotron X-ray irradiation can modify the local structure of WO3 nanoparticles during the XAS experiment and should be considered when interpreting EXAFS data for radiation-sensitive nanoscale oxides.
References
[1] X. Dong et al., J. Photochem. Photobiol. C Photochem. Rev. 53 (2022) 100555.
[2] Y. Badour et al., J. Electron. Mater. 51 (2022) 1555.
[3] W. A. Caliebe et al., AIP Conf. Proc. 2054 (2019) 060031.
[4] J. Timoshenko et al., J. Phys.: Condens. Matter 26 (2014) 055401.
