Molten salt synthesis of neodynium oxyfluoride with tetragonal structure

Abstract

Neodynium oxyfluoride has been applied for luminescence materials and solid electrolytes because of its structure combined advantages of rare-earth cations with F− and O2− anions. Since the neodynium oxyfluoride with tetragonal structure retains a defect structure having anion vacancies where anions transfer, it shows higher anion conductivity than that with cubic and rhombohedral structures. The feasibility of synthesizing tetragonal neodynium oxyfluoride in molten fluorides was investigated in this work. The neodynium oxyfluoride was not dissolved in molten LiF–CaF2 based on the in-situ observation using confocal scanning laser microscope, therefore neodynium oxyfluoride can be easily collected from molten fluorides. The neodynium oxyfluoride with tetragonal structure was successfully synthesized by the reaction of Nd2O3 with molten fluorides. The synthesis process was analyzed by differential scanning calorimetry combining X-ray diffraction and scanning electron microscope. The reaction model was described and the reaction rate constant was calculated. According to the mathematical description of kinetic equation, the reaction rate could be proportional to the interface difference between molten fluorides and solid Nd2O3.