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Microwave-Assisted Synthesis, Characterization, and Thermal Decomposition of Rare-Earth Metal Disulfides RES2 (RE = La, Pr, Nd)



Microwave-assisted metathesis reactions from anhydrous rare-earth metal trichlorides and alkali metal polychalcogenides in dimethylformamide in the temperature interval 160 °C ≤ T ≤ 220 °C yield sub-micron and nanometer scaled particles of the rare-earth metal disulfides RES2 (RE = La, Pr, Nd). The samples were characterized by X-ray powder diffraction, electron microscopy, chemical analysis, and Raman and UV/Vis spectroscopy. The products adopt the monoclinic α-RES2 type (space group P21/a) and form desert rose-like agglomerates. The nano-scaled samples show significantly reduced optical bandgaps compared to the bulk material. The thermal decomposition in air at 550 °C ≤ T ≤ 1000 °C yields rare-earth metal oxide sulfates RE2O2SO4.