Thermal and phase analysis in the (LiF-NaF)eut-LnF3 (Ln = Sm, Gd, and Nd) molten systems

Abstract Phase equilibria and thermal behavior of molten ternary systems (LiF–NaF)eut–LnF3 (Ln = Sm, Gd, and Nd) were investigated using classical thermal analysis and X-ray powder diffraction (XRPD). The phase diagrams were determined in the concentration range up to 40 mol% LnF3, with the aim of identifying primary crystallization fields and eutectic transitions. Thermal effects such as primary and secondary crystallization, as well as eutectic temperatures, were recorded and used to construct schematic pseudo-binary phase diagrams. The XRPD analysis confirmed the presence of known ternary and binary fluoride phases, including NaLnF4 (Ln = Sm, Gd, and Nd), and, in the Gd system, LiGdF4. The results reveal common structural features among the systems, including distinct solid solution fields and consistent phase relationships, while also highlighting specific differences in compound formation and thermal behavior. These findings contribute to a deeper understanding of lanthanide fluoride systems relevant for applications in molten salt technologies and rare-earth material processing.