Unraveling Element-Selective Local Structures in Multielement Alloy Nanoparticles with EXAFS.

We demonstrate physically consistent and interpretable extended X-ray absorption fine structure (EXAFS) curve-fitting analyses for estimating element-selective local structures in multielement alloy nanoparticles (MEA NPs). The difficulty in analyzing multielement systems originates from the too large number of independent structural parameters to fit, far exceeding the information content of the typical experimental data. Herein, this challenge is overcome by simultaneously fitting multiple data at different absorption edges and temperatures while imposing constraints based on a physically reasonable model. Another advantage of our approach is interpretability; the individual contributions of the constituent elements to the static and dynamic structures are explicitly estimated as atomic radii and Einstein temperatures. This method is used to analyze MEA NPs composed of platinum-group metals and -block metals, which have contrasting properties, including atomic radii, melting points, and electronegativities. The results indicate that the local structures reflect the intrinsic nature of the elements and are also influenced by the interactions among them. The local structures around the -block metals in the MEA NPs are shown to be distinctively modulated compared with those in the corresponding monometals, which is attributed to the electronic interaction with the platinum-group metals based on calculations. Our method is expected to facilitate the experimental characterization of these structurally complicated nanomaterials, which have been analyzed relying on calculations, yielding more precise pictures of real systems for investigating structure-property relationships.