  Tellurium trioxide, TeO3, is the only example of a trioxide adopting at
ambient conditions the VF3-type structure (a distorted variant of the cubic
ReO3 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 experiment the
ambient-pressure VF3-type structure (R-3c symmetry) is preserved up to 110 GPa.
In contrast, calculations indicate that above 66 GPa the R-3c structure should
transform to a YF3-type polymorph (Pnma symmetry) with the coordination number
of Te6+ 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 WO3. The YF3-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. We analyse the influence of pressure on
the band gap of TeO3, and discuss the present findings in the context of
structural transformations of trioxides and trifluorides adopting an extended
structure in the solid state
