Resolving and Quantifying Nanoscaled Phases in Amorphous FeF3 by Pair Distribution Function and Mossbauer Spectroscopy

Probing the atomic structure of materials displaying a lack of long-range order has been a continuous challenge for the material science's community. X-ray amorphous Fe(F)3 has been shown to be a promising electrode material in Li and Na ion batteries. Providing structural information on this class of compounds is therefore of interest as it can help rationalize the material's properties and further enabled its optimization. Herein, we used the pair distribution function and Mossbauer spectroscopy to provide unique insights into the atomic structure of amorphous FeF3. The results showed that amorphous FeF3 contained two phases built from corner-sharing of FeF6 octahedra. According to X-ray diffraction data, the PDF was successfully modeled based on two structural models related to the distorted ReO3 and the hexagonal-tungsten-bronze networks of FeF3. The lack of long-range order shown by conventional XRD data and PDF analysis was shown to arise mostly from disorder. This study provides detailed atomic structure with corresponding spectroscopic signature of amorphous phases. Quantitative analysis of both techniques indicated similar trends. This showed that our approach can be employed to determine the structure of other complex materials.