The preparation and characterization of Ba3Te2O9; a new oxide structure

The structure of Ba₃Te₂O₉ has been determined from x-ray powder diffraction data and by profile refinement of neutron diffraction data. We find tellurium octahedrally coordinated as expected and the same face-shared [B₂O₉]^6? unit as observed in Ba₃W₂O₉. The phase Ba₃Te₂O₉ has, however, a Cs₃Fe₂F₉ type structure ($\text{P}\text{6}{}_3\text{mmc}$, $\text{a}\text{=}\text{5}\text{.8603(1)}\text{A}\text{?}$, $\text{c}\text{=14.3037(6)}\text{A}\text{?}$) rather than the Cs₃Tl₂Cl₉ structure (R3c) found for the tungsten analogue. The two oxide structures have the same BaO₃ layer sequence but differ only in the spatial arrangement of the [B₂O₉] groups in the lattice. Infrared and Raman spectra confirm the different site symmetries associated with the different packing of the tungstate and tellurate anions in their respective structures.