X-ray powder diffraction data and Rietveld refinement for Ln 6 WO 12 ( Ln = Y , Ho )

The crystal structure of the two isostructural rare earth tungstates Ln 6 WO 12 ( Ln = Y , Ho ) has been refined by the Rietveld method from X-ray powder diffraction data. They crystallize with a three-dimensional rhombohedral structure (S.G. R 3¯ and Z =3 for the R -centered setting) closely related to that of the binary oxides Ln 7 O 12 and deriving from the ideal fluorite structure. Final refinements, with isotropic thermal motion for each atom, resulted in profile and structure factors R wp =0.166, R F =0.037 with Ln = Y and R wp =0.121, R F =0.040 with Ln = Ho . The rare earth element is sevenfold coordinated with Ln–O bond lengths ranging from 2.19 to 2.70 Å for Y 6 WO 12 and from 2.18 to 2.68 Å for Ho 6 WO 12 ; the coordination polyhedron may be described as a monocapped trigonal prism. The tungsten atom is located at the center of a WO 6 octahedron with a unique W–O distance of 1.98 and 1.92 Å for Y 6 WO 12 and Ho 6 WO 12 , respectively.