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Under DAPHNE4NFDI, the X‐ray absorption spectroscopy (XAS) reference database, RefXAS, has been set up. For this purpose, we developed a method to enable users to submit a raw dataset, with its associated metadata, via a dedicated website for inclusion in the database. Implementation of the database includes an upload of metadata to the scientific catalogue and an upload of files via object storage, with automated query capabilities through a web server and visualization of the data and files. Based on the mode of measurements, quality criteria have been formulated for the automated check of any uploaded data. In the present work, the significant metadata fields for reusability, as well as reproducibility of results (FAIR data principles), are discussed. Quality criteria for the data uploaded to the database have been formulated and assessed. Moreover, the usability and interoperability of available XAS data/file formats have been explored. The first version of the RefXAS database prototype is presented, which features a human verification procedure, currently being tested with a new user interface designed specifically for curators; a user‐friendly landing page; a full list of datasets; advanced search capabilities; a streamlined upload process; and, finally, a server‐side automatic authentication and (meta‐) data storage via MongoDB, PostgreSQL and (data‐) files via relevant APIs. [ABSTRACT FROM AUTHOR]

The studies of polaronic centers in a homologous series of scheelite-type compounds A WO 4 ( A = Ca, Sr, Ba) were performed using the W L 3 -edge and Sr K-edge X-ray absorption spectroscopy combined with the reverse Monte Carlo simulations, X-ray photoelectron spectroscopy (XPS), and first-principles calculations. Protonated scheelites H x A WO 4 were produced using acid electrolytes in a one-step route at ambient conditions. The underlying mechanism behind this phenomenon can be ascribed to the intercalation of H + into the crystal structure of tungstate, effectively resulting in the reduction of W 6+ to W 5+ , i.e., the formation of polaronic centers, and giving rise to a characteristic dark blue-purple color. The emergence of the W 5+ was confirmed by XPS experiments. The relaxation of the local atomic structure around the W 5+ polaronic center was determined from the analysis of the extended X-ray absorption fine structures using the reverse Monte Carlo method. The results obtained suggest the displacement of the W 5+ ions from the center of [W 5+ O 4 ] tetrahedra in the structure of A WO 4 scheelite-type tungstates. This finding was also supported by the results of the first-principles calculations.