A new form of Cd(3)TeO(6) revealing dimorphism

Phase-formation studies in the system CdO–TeO(3) using a CsCl/NaCl melt at comparatively low temperatures revealed that tricadmium orthotellurate(VI), Cd(3)TeO(6), is dimorphic. The new modification of Cd(3)TeO(6) is denoted as the β-form and adopts the rhombohedral Mg(3)TeO(6) structure type with one Cd and two O sites in general positions, and two Te sites with site symmetry [Image: see text] each. In comparison with the previously reported monoclinic cryolite-type α-form that was prepared at higher temperatures, β-Cd(3)TeO(6) has a much lower density and most likely represents a metastable modification. Whereas the [TeO(6)] octa­hedra in both polymorphs are very similar and show only minor deviations from ideal values, the polyhedra around the Cd(II) sites are different, with a distorted [CdO(6)] octa­hedron in both modifications but an additional [CdO(8)] polyhedron with a [4 + 4] coordination in the α-form.