Syntheses, structure, magnetism, and optical properties of the partially ordered quaternary interlanthanide sulfides PrLnYb2S6 (Ln=Tb, Dy)

Dark red single crystals of PrLnYb2S6 (Ln=Pr/Yb, Tb, Dy) have been synthesized through the reactions of elemental rare earth metals and S using a Sb2S3 flux at 1000 °C. These isotypic compounds adopt the F-Ln2S3 three-dimensional open-channel structure type. Eight-coordinate Pr3+ ions sit in the channels that are constructed from three different edge-shared double chains running down the b-axis that contain Yb(1)S6 octahedra, Yb(2)S6 octahedra, and LnS7 monocapped trigonal prisms. Each double chain connects to four other neighbors by sharing vertices and edges. Considerable disordering in Ln positions was observed in single X-ray diffraction experiments only in the case of Pr/Yb. Least-squares refinements gave rise to the formulas of Pr1.34Yb2.66S6, of PrTbYb2S6, and PrDyYb2S6, which are confirmed by the elemental analysis and magnetic susceptibility measurements. Pr1.34Yb2.66S6, PrTbYb2S6, and PrDyYb2S6 are paramagnetic down to 2 K, without any indications of long-range magnetic ordering. The optical transitions for Pr1.34Yb2.66S6, PrTbYb2S6, and PrDyYb2S6 are at approximately 1.6 eV. Crystallographic data are listed as an example for PrTbYb2S6: monoclinic, space group P21/m, a=10.9496(10) Å, b=3.9429(4) Å, c=11.2206(10) Å, β=108.525(2)°, V=459.33(7) Å3, Z=2.