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)W O(12) (Ln=Y, Ho) has been refined by the Rietveld method from X-ray powder diffraction data. They crystallize with a three-dimensional rhombohedral st ructure (S.G. R (3) over bar and Z=3 for the R-centered setting) closely re lated to that of the binary oxides Ln(7)O(12) and deriving from the ideal f luorite structure. Final refinements. with isotropic thermal motion for eac h atom, resulted in profile and structure factors R-wp=0.166, R-F=0.037 wit h Ln=Y and R-wp=0.121, R-F=0.040 with Ln=Ho. The rare earth element is seve nfold coordinated with Ln-O bond lengths ranging from 2.19 to 2.70 Angstrom for Y6WO12 and from 2.18 to 2.68 Angstrom for Ho6WO12; the coordination po lyhedron may be described as a monocapped trigonal prism. The tungsten atom is located at the center of a WO6 octahedron with a unique W-O distance of 1.98 and 1.92 Angstrom for Y6WO12 and Ho6WO12 respectively. (C) 2000 Inter national Centre for Diffraction Data. [S0885-7156(00)00504-2].