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Rapid Molten Salt Synthesis of Isotropic Negative Thermal Expansion ScF3



With a simple ReO3-type structure, ScF3 exhibits a rare property of isotropic negative thermal expansion over a large temperature range. In this study, a rapid and low-temperature synthesis route has been developed to prepare pure phase of ScF3 in which NaNO3 or KNO3 as reaction media and Sc(NO3)3 and NH4HF2 as precursors (i.e., 30 min and 310°C). The sample of ScF3 has relatively regular morphology and shows high crystallinity as well as single-crystalline nature. The type of molten salts has obvious impact on morphologies of the particles. Substituting NaNO3 with KNO3, cubes of ScF3 turns to be nanosticks. The thermal stability of the as-prepared ScF3 was investigated by thermal analysis. Molten salts play a significant role in eliminating the nonstoichiometric impurity of ScF2.76 which is a common impurity during the conventional chemical reaction. This study reveals that molten salt is in favor of preparing those fluorides and relatives which is inert with moisture.