Synthesis and characterization of the rare-earth vanadium oxyselenides Ln7VO4Se8 (Ln = Nd, Sm, Cd)

The new compounds Ln(7)VO(4)Se(8) (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) Angstrom, b = 15.5528(10) Angstrom, c = 3.9948(3) Angstrom; Sm7VO4Se8, a = 14.200(2) Angstrom, b = 15.451(2) Angstrom, c = 3.9511(6) Angstrom; Gd7VO4Se8, a = 14.075(8) Angstrom, b = 15.424(6) Angstrom, c = 3.903(1) Angstrom. 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. (C) 2000 Academic Press.