High-pressure phase transition of AB 3 -type compounds: case of tellurium trioxide.

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). 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. In experiments the ambient-pressure VF 3 -type structure ( R 3̄ c symmetry) is preserved up to 110 GPa. In contrast, calculations indicate that above 66 GPa the R 3̄ 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. 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 . The YF 3 -type phase is predicted to be stable up to 220 GPa when it should transform to a novel structure of R 3̄ symmetry and Z = 18. 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.