The structure of TiO2-SiO2 and CaO-SiO2 sol-gel glasses from neutron diffraction and solid state NMR using isotopic enrichment of titanium, calcium and oxygen

An advanced materials characterisation methodology has been used to examine systematically a range of sol-gel glass materials of contemporary interest. Neutron diffraction using Ti-46 and Ti-48 stable isotopes, and isotope-enriched O-17 MAS NMR, have been used to characterise the structure of catalytically active (TiO2)(x)(SiO2)(1-x) sol-gel glass as a function of calcination temperature (T=250, 500 and 750 degrees C). The results reveal directly two Ti-O distances in a homogeneous (TiO2)(0.18)(SiO2)(0.82) sol-gel derived glass. The detailed nature of the Ti environment may be discerned from a combination of neutron scattering data with solid state NAIR, including the possible presence of phase separation at the higher temperature. Neutron diffraction Using Ca-44, and isotope enriched O-17 MAS NMR have also been used to study the detailed nature of the structure of CaO-SiO2 bioactive sol-gel glasses. The results offer a direct observation of multiple Ca-O distances in this material, and pave the way to a fuller understanding of the role of Ca in its bioactivity. The results presented here are consistent with, but greatly extend our previous XRD, O-17 and Si-29 MAS-NMR, XANES and EXAFS studies of these materials.