Valence evolution of samarium in magnesium-driven reduction of SmF 3

The preparation of metallic samarium through metallothermic reduction is complicated by its variable valence characteristics. This study employed SmF 3 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 SmF 3 by Mg to form SmF 2 is spontaneous, whereas the formation of metallic Sm is thermodynamically unfavorable. Experimental results demonstrate that at Mg/SmF 3 molar ratios of 0.5, 1.0, and 1.5, the reduction primarily yields Sm 3 F 7 and MgF 2 , while increasing the ratio to 2.0 leads to additional formation of SmMgF 4 . Importantly, varying the Mg/SmF 3 molar ratio does not alter the valence states of samarium in the final products. XPS analysis reveals the coexistence of Sm 3+ and Sm 2+ in all products with a consistent ratio of ∼9:1, where adsorbed oxygen promotes Sm 2+ oxidation. These findings provide important insights for controlling valence states in samarium alloy preparation via metallothermic reduction.