New routes to alkali-metal–rare-earth-metal sulfides

Abstract

Ternary alkali-metal–rare-earth-metal sulfides, MRES₂(M = Li, Na, K; RE = Y, La–Yb) were prepared by heating RECL₃and M₂S under an H₂S–N₂ atmosphere at 750–800 °C for 10 min. The ternary sulfides form thin, mostly coloured plates. The structures were characterised by X-ray powder diffraction, which revealed high-temperature cubic modifications for LiHoS₂ and LiErS₂. The disordered cubic form (NaCl type) was observed for LiLnS₂(Ln = Pr–Er) and NaLnS₂(Ln = La–Nd), while the ordered rhombohedral form (α-NaFeO₂ type) was observed for LiYbS₂, NaLnS₂(Sm–Yb) and KLnS₂(La–Yb). Alkali-metal–rare-earth-metal sulfides may also be synthesized from the rare-earth-metal chloride and alkali-metal halide under comparable conditions. Similarly, thermolysis of the rare-earth-metal sesquisulfide (γ-RE₂S₃), oxysulfide (RE₂O₂S) or oxychloride (REOCL) with M₂S or MCI in an atmosphere of H₂S-N₂ gives MRES₂. The materials were characterised by powder X-ray diffraction, scanning electron microscopy (SEM), energy dispersive analysis by X-rays (EDXA), Raman, infrared, magnetic moments and microanalysis.