Synthesis, physical and optical properties, and electronic structure of the rare-earth oxysulfides Ln2O2S (Ln=Sm, Eu)

Abstract The compounds Ln 2 O 2 S (Ln=Sm, Eu) were prepared from the respective oxides by partial sulfurization under flowing CS 2 /Ar/O 2 atmosphere. The main feature of the structure is the packing of S 2− and O 2− anions with Ln 3+ located in the center of a capped octahedron. Electrical conductivity measurements on pressed pellets showed that both phases are highly resistive with conductivities lower than 10 −8  S cm −1 at room temperature. The optical bandgaps were assessed at 4.2 and 4.4 eV for Sm 2 O 2 S and Eu 2 O 2 S, respectively. Electronic structure calculations were performed by means of extended Huckel tight-binding method. The insulating properties are in good agreement with the results predicted by theoretical calculations.