Direct evidence for trivalent titanium in artificially irradiated (electrons) oxide glasses

Ti-doped borosilicate and disilicate glasses were irradiated with high-energetic electrons in order to study Ti(IV) reduction processes. Reduction efficiency was actually confirmed by an important Ti(III) EPR signal around g=1.93 in irradiated samples. The Ti(III) amount increases with the irradiation dose. Moreover, the Ti(III) environment depends on the glass composition. Hence, the reduction process efficiency is strongly correlated to the Ti(IV) environment in the pristine glass. The Ti environment was analyzed by Ti K-edge XANES in order to understand the reduction mechanisms. Pre-edge analysis of non-irradiated samples indicates the presence of four, five and six coordinated tetravalent Ti sites in borosilicate glasses, whereas in disilicate the Ti(IV) coordination is a mixture between five-fold and six-fold. In irradiated samples, the Ti pre-edge shows a slight low-energy shift associated to an intensity decrease in disilicate glasses. Correlation between EPR and XANES experiments allows for interpretation of the pre-edge variation in terms of Ti(III) formation. Profiles (μm resolution) were also performed to measure the proportion of Ti(III) on different points across the irradiated DS. No significant difference in XANES spectra was observed suggesting that the production of Ti(III) is homogeneous in the volume.