Titanium coordination in silicate glasses investigated using OK-edge X-ray absorption spectroscopy

A series of titanium silicate glasses along the composition joins TiO2-SiO2, TiO2-Na2SiO3, TiO2K2SiO3 and TiO2-CaSiO3, has been examined using oxygen K-edge X-ray absorption near edge structure spectroscopy (XANES) confined to the near-surface region. Sharp pre-edge features in the spectra can be used to determine the Ti coordination in the glasses. The presence of Ti-[4] is indicated by a pre-edge peak at similar to534 eV while Ti-[5] is indicated by a peak at similar to533 eV. Titanium exists in all these glasses as Ti-[4] and Ti-[5] with no Ti-[5] being present. For alkali-containing glasses the Ti-[5] site becomes more prevalent with increasing TiO2. TiO2-K2SiO3 compositions contain a greater proportion of Ti-[4] than comparable Na2O compositions. This is consistent with earlier Ti L-edge findings. The TEY spectra for the TiO2-CaSiO3 compositions indicate the presence of significant amounts of Ti-[5] at high TiO2 contents; however, comparison of TEY (near surface) and FY (bulk sample) XANES shows that the Ti-[5] is confined to the surface of the glass sample with the bulk of the glass containing Ti-[4].