Raman and density functional theory studies of lutecium fluoride and oxyfluoride structures in molten FLiNaK.

Abstract Combined with Raman spectroscopy and density functional theory (DFT) calculations, the micro-structures in molten FLiNaK-LuF3 and FLiNaK-LuF3-Li2O systems were studied. Both LuF52− (D3h) and LuF63− (Oh) anions were identified in molten FLiNaK, and their relative content varied with the concentration of LuF3. For regarding the affection of oxygen anion, Li2O was added into the molten FLiNaK-LuF3 (20 mol%) sample. The lutecium oxyfluoride anion Lu2OF84− was firstly formed which possesses a linear Lu O Lu geometry with two LuF4 moieties bridged by one single oxygen atom. Further increasing the Li2O content to 10 mol% resulted in the formation of two species, which belonged to the Lu2O2F42− and Lu2O2F64− anions. When increased the concentration of Li2O to 20 mol%, a new species appeared which was approximate to the oxide structure.