Zur Synthese und Struktur ternärer Chalcogenide der Seltenen Erden AlnX 2 mit A ≙ alkalimetall und X ≙ Schwefel, Selen oder Tellur

Abstract

The sulfides RbLnS 2 and CsLnS 2 were synthesized by heating alkali carbonate and the respective rare earth oxides under an H 2S atmosphere at 1000 °C. The ternary sulfides form thin, mostly coloured plate-like crystals. The structures of the cesium compounds and RbCeS 2 were characterized by X-ray investigations on single crystals. All the compounds crystallize with the α-NaFeO 2 structure type; for CsLnS 2 compounds with Ln ≙ PrLu the βRbScO 2 structure type was found as a second modification. This was proven by a single crystal X-ray investigation on CsPrS 2. The samarium compounds NaSmSe 2, KSmSe 2, NaSmTe 2, KSmTe 2, and RbSmTe 2 were prepared as examples for the corresponding selenides and tellurides. Syntheses were done by reacting the elements in a closed system. These chalcogenides also crystallize with the α-NaFeO 2 structure type. NaSmSe 2 shows an additional low temperature modification with a statistical distribution of the cations. For KSmTe 2 the structural determination was carried out on a single crystal. The sequence of the lattice constants and the ζ-parameters of the sulfur atoms will be discussed in accordance to their dependence on the lanthanide contraction.