Synthesis and Characterization of the Rare-Earth Vanadium Oxyselenides Ln7VO4Se8 (Ln=Nd, Sm, Gd)

The new compounds Ln7VO4Se8 (Ln=Nd, Sm, Gd) were each prepared by heating V, Se, and the corresponding rare-earth sesquioxide at 1223 K in a sealed fused-silica tube. Single crystals have been grown through the use of an antimony flux. They have been characterized by single-crystal and powder X-ray diffraction measurements and by energy dispersive X-ray analysis. These isostructural compounds crystallize with two formula units in the orthorhombic space group Pbam in cells (at 153 K) of dimensions: Nd7VO4Se8, a=14.3419(9) ?, b= 15.5528(10) ?, c=3.9948(3) ?; Sm7VO4Se8, a=14.200(2) ?, b=15.451(2) ?, c=3.9511 (6) ?; Gd7VO4Se8, a=14.075(8) ?, b=15.424(6) ?, c=3.903(1) ?. The new structure type comprises four crystallographically independent Ln atoms with three different coordination geometries and one V atom in an octahedral environment. Magnetic measurements reveal that Gd7VO4Se8 is paramagnetic down to 5 K.