Investigation of the local structure of molten ThF₄–LiF and ThF₄–LiF–BeF₂ mixtures by high-temperature X-ray absorption spectroscopy and molecular-dynamics simulation

The microscopic structures of ThF₄–LiF and ThF₄–LiF–BeF₂ molten salts have been systematically investigated by in situ high-temperature X-ray absorption fine-structure (XAFS) spectroscopy combined with molecular-dynamics (MD) simulations. The results reveal that the local structure of thorium ions was much more disordered in the molten state of the ThF₄–LiF–BeF₂ salt than that in ThF₄–LiF, implying that the Th and F ions were exchanged more frequently in the presence of Be ions. The structures of medium-range-ordered coordination shells (such as Th–F_2nd and Th–Th) have been emphasized by experimental and theoretical XAFS analysis, and they play a significant role in transport properties. Using MD simulations, the bonding properties in the molten ThF₄–LiF and ThF₄–LiF–BeF₂ mixtures were evaluated, confirming the above conclusion. This research is, to the best of our knowledge, the first systematic study on the ThF₄–LiF–BeF₂ molten salt via quantitative in situ XAFS analysis and MD simulations.