3 In these systems tellurium is found as an anion (Te 2−), but materials containing this element as a cation are also of great interest, as exemplified by the acousto-optic and nonlinear optoelectronic properties of tellurium dioxide (TeO 2).

Tellurium, one of the heaviest metalloids, has recently attracted significant attention due to its role in manufacturing highly efficient photovoltaic panels, 1,2 and investigations of superconductivity in iron-based compounds. We analyse the influence of pressure on the band gap of TeO 3, and discuss the present findings in the context of structural transformations of trioxides and trifluorides adopting an extended structure in the solid state. The YF 3-type phase is predicted to be stable up to 220 GPa when it should transform to a novel structure of R 3 ̄ symmetry and Z = 18. The lack of this transition in the room-temperature experiment is most probably connected with energetic barriers, in analogy to what is found for compressed WO 3. In contrast, calculations indicate that above 66 GPa the R 3 ̄ c structure should transform to a YF 3-type polymorph ( Pnma symmetry) with the coordination number of Te 6+ increasing from 6 to 8 upon the transition. In experiments the ambient-pressure VF 3-type structure ( R 3 ̄ c symmetry) is preserved up to 110 GPa. Here we present a combined experimental (Raman scattering) and theoretical (DFT modelling) study on the influence of high pressure (exceeding 100 GPa) on the phase stability of this compound. Tellurium trioxide, TeO 3, is the only example of a trioxide adopting at ambient conditions the VF 3-type structure (a distorted variant of the cubic ReO 3 structure).

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