Search

A comparison is made between the three principal methods for analysis of neutron and X-ray diffraction data from noble gas fluids by direct Fourier transform. All three methods (standard Fourier transform, Lorch modification and Soper-Barney modification) are used to analyse four different sets of diffraction data from noble gas fluids. The results are compared to the findings of a full-scale real space structure determination, namely Empirical Potential Structure Refinement. Conclusions are drawn on the relative merits of the three Fourier transform methods, what information can be reliably obtained using each method, and which method is most suitable for analysis of different kinds of diffraction data. The mathematical validity of the Lorch method is critically analysed., Comment: Including supplementary information

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