K3LaTe2O9: a new alkali-rare earth tellurate with face-sharing TeO6 octahedra.

A new quaternary alkali-lanthanide metal tellurate K3LaTe2O9 has been synthesized by a conventional high-temperature solid state method, and single crystals have been grown by spontaneous crystallization. K3LaTe2O9 crystallizes in the hexagonal space group P63/mmc, with a = b = 6.0589(9) Å, c = 15.024(3) Å, and Z = 2. In the structure, [Te2O9](6-) contains rare face-sharing TeO6 polyhedra, which are connected by LaO6 octahedra forming a three-dimensional framework structure. Furthermore, its properties are investigated by UV-vis-NIR diffuse reflectance spectroscopy, Raman and IR spectroscopy, thermal analysis, variable-temperature X-ray powder diffraction, and first-principles calculations.