Syntheses, structure, magnetism, and optical properties of the partially ordered quaternary interlanthanide sulfides Pr LnYb 2S 6 ( Ln=Tb, Dy)

Abstract

Dark red single crystals of Pr LnYb 2S 6 ( Ln=Pr/Yb, Tb, Dy) have been synthesized through the reactions of elemental rare earth metals and S using a Sb 2S 3 flux at 1000 °C. These isotypic compounds adopt the F- Ln 2S 3 three-dimensional open-channel structure type. Eight-coordinate Pr 3+ ions sit in the channels that are constructed from three different edge-shared double chains running down the b-axis that contain Yb(1)S 6 octahedra, Yb(2)S 6 octahedra, and LnS 7 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 Pr 1.34Yb 2.66S 6, of PrTbYb 2S 6, and PrDyYb 2S 6, which are confirmed by the elemental analysis and magnetic susceptibility measurements. Pr 1.34Yb 2.66S 6, PrTbYb 2S 6, and PrDyYb 2S 6 are paramagnetic down to 2 K, without any indications of long-range magnetic ordering. The optical transitions for Pr 1.34Yb 2.66S 6, PrTbYb 2S 6, and PrDyYb 2S 6 are at approximately 1.6 eV. Crystallographic data are listed as an example for PrTbYb 2S 6: monoclinic, space group P2 1 /m, a=10.9496(10) Å, b=3.9429(4) Å, c=11.2206(10) Å, β=108.525(2)°, V=459.33(7) Å 3, Z=2.