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

摘要

A series of titanium silicate glasses along the composition joins TiO₂–SiO₂, TiO₂–Na₂SiO₃, TiO₂–K₂SiO₃ 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 [4]Ti is indicated by a pre-edge peak at ~534 eV while [5]Ti is indicated by a peak at ~533 eV. Titanium exists in all these glasses as [4]Ti and [5]Ti with no [6]Ti being present. For alkali-containing glasses the [5]Ti site becomes more prevalent with increasing TiO₂. TiO₂-K₂SiO₃ compositions contain a greater proportion of [4]Ti 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 [5]Ti at high TiO₂ contents; however, comparison of TEY (near surface) and FY (bulk sample) XANES shows that the [5]Ti is confined to the surface of the glass sample with the bulk of the glass containing [4]Ti.