Structure of (Ta2O5)(x)(SiO2)(1-x) xerogels (x=0.05, 0.11, 0.18, 0.25 and 1.0) from FTIR, Si-29 and O-17 MAS NMR and EXAFS

A combination of Si-29 and O-17 MAS NMR, EXAFS and FT-IR spectroscopy has been used to study the atomic structure of (Ta2O5)(x)(SiO2)(1 - x) (x = 0.05, 0.11, 0.18 and 0.25) xerogels prepared by reacting partially-hydrolysed tetraethyl orthosilicate with tantalum(V) ethoxide. Amorphous tantala, a-Ta2O5, xerogels have also been prepared and their structures studied in detail for the first time. Results have shown that in all these materials, Ta adopts predominantly 5-fold coordination with respect to oxygen. For the mixed oxide xerogels, partial phase separation of the two component oxides occurs for x > 0.11