Sulfures de type U 3S 5 formes par l'uranium et les terres rares Ln III2US 5 ( [formula omitted]) et Ln IIU 2S 5 (Ln II = Sm II et Eu II), et leurs solutions solides

Abstract

The trivalent rare earth sulfides (La to Gd, Eu excepted), combine with US 2 and give Ln 2US 5 orthorhombic sulfides, spatial group Pnma, U 3S 5-type. The crystal structure of Sm III 2US 5 is established from single crystals determinations (R = 0,05) : the atomic positions are identical to those of U 3S 5. These compounds form continuous solid solutions with U 3S 5 by substitution of Ln III by U III, and partial solid solutions with US 2 by a mechanism involving substitution of Ln III by U IV and vacancies. The two compounds Eu IIU 2S 5 and Sm IIU 2S 5 are isostructural with the preceding ones, from a single crystal study. A continuous passage from Sm III 2US 5 to Sm IIU 2S 5 and to U 3S 5 is observed.