Calciothermic Reduction Reaction Behavior and Samarium Ion Valence Evolution of SmF₃

Samarium is a rare earth element that exhibits variable valence states of + 2 and + 3. In this work, we present the reduction products obtained through calciothermic reduction of SmF₃ at various molar ratios of Ca to SmF₃. The crystal structure, morphology, elemental distribution, and chemical valence of the reduction products were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The results show that SmF_2.028 and CaF₂ are the sole reduction products obtained under molar ratios of 0.5, 1, 1.5, and 2 for Ca to SmF₃, whereas some unreacted metallic Ca is detected in the products at a molar ratio of Ca to SmF₃ of 2. The samarium ions in the reduction products exhibit mixed valence states with a relative content of approximately 9:1 for Sm³⁺ and Sm²⁺. Notably, the large amount of adsorbed oxygen present in the products oxidizes Sm²⁺ to Sm³⁺.