Valence evolution of samarium in magnesium-driven reduction of SmF₃.

The preparation of metallic samarium through metallothermic reduction is complicated by its variable valence characteristics. This study employed SmF₃ as precursor for magnesium thermal reduction. The reduction products were thoroughly characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) to determine the crystal structure, morphology, elemental distribution, and chemical valence states. Thermodynamic calculations indicate that the reduction of SmF₃ by Mg to form SmF₂ is spontaneous, whereas the formation of metallic Sm is thermodynamically unfavorable. Experimental results demonstrate that at Mg/SmF₃ molar ratios of 0.5, 1.0, and 1.5, the reduction primarily yields Sm₃F₇ and MgF₂, while increasing the ratio to 2.0 leads to additional formation of SmMgF₄. Importantly, varying the Mg/SmF₃ molar ratio does not alter the valence states of samarium in the final products. XPS analysis reveals the coexistence of Sm³⁺ and Sm²⁺ in all products with a consistent ratio of ∼9:1, where adsorbed oxygen promotes Sm²⁺ oxidation. These findings provide important insights for controlling valence states in samarium alloy preparation via metallothermic reduction. [ABSTRACT FROM AUTHOR]