NEW ROUTES TO ALKALI-METAL-RARE-EARTH-METAL SULFIDES

Ternary alkali-metal-rare-earth-metal sulfides, MRES2 (M = Li, Na, K; RE = Y, La-Yb) were prepared by heating RECl3 and M2S under an H2S-N2 atmosphere at 750-800-degrees-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 (alpha-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 (gamma-RE2S3), oxysulfide (RE2O2S) or oxychloride (REOCl) with M2S or MCl 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.