In Situ High Temperature Raman and DFT Analysis of LiF-PrF3-Pr6O11 Molten Salt System

Understanding the structural intricacies of LiF-PrF3-Pr6O11 molten salts is of paramount importance for advancing praseodymium electrolysis technology. In this study, the ion structure of the LiF-PrF3-Pr6O11 molten salt system was analyzed by combining in situ high temperature Raman spectroscopy and density functional theory (DFT) within the temperature range of 1203 similar to 1323K. Additionally, the ions present in the melt were quantitatively analyzed using Raman scattering cross section (RSCS). The results indicate the presence of PrF63- (O-h), Pr2F82- (C-1), Pr2F93- (S-4), and Pr2F104- (D-2h) praseodymium fluoride anions in the LiF (15 wt pct)-PrF3 (85 wt pct) melt. The predominant ions in the melt transform from Pr2F82- and Pr2F104- to PrF63- and Pr2F93- with increasing temperature. The PrOF32- (C-1), PrOF54- (C-4v), Pr2OF62- (C-2v), and Pr2OF84- (C-2) praseodymium oxyfluoride anions were formed after 2wt pct Pr6O11 was added to the LiF-PrF3 molten salt. The stability of praseodymium fluoride ions decreases as the temperature rises, resulting in the conversion of these ions in the molten state into Pr2OF62- and Pr2OF84- anions.