A Ti L-edge X-ray absorption study of Ti-silicate glasses

A series of titanium silicate glasses along the composition joins SiO2-TiO2, Na2SiO3-TiO2, K2SiO3- TiO2, and CaSiO3-TiO2 have been examined using titanium (Ti) L-edge X-ray absorption near-edge spectroscopy (XANES). XANES spectra were collected at the Canadian Synchrotron Radiation Facility (CSRF), University of Wisconsin, Madison, using the Spherical Grating Monochromator (SGM) beamline. Glass spectra were compared with spectra obtained from crystalline analogues with differing Ti coordination environments: beta(r)Ba(2)TiO(4) (Ti-[4]); fresnoite (Ti-[5]); and rutile and anatase (Ti-[6]). The Ti L-edge data indicate that for homogeneous TiO2-SiO2 glasses Ti coordination is Ti-[5] at TiO2 contents below 3.6 wt% but predominantly Ti-[4] with some Ti-[5] present above this content. There is no evidence for Ti-[6]. For the Na-2 O-containing glasses the L-edge data indicate that Ti is Ti-[4] with some Ti-[5] at low TiO2 contents, becomes a mix of Ti-[4] and Ti-[5] with increasing TiO2 content, but is exclusively Ti-[5] by 14.3 wt% TiO2. The K2O composition glasses exhibit similar behavior but contain a greater proportion of Ti-[4] and less Ti-[5] than the equivalent Na2O-bearing glasses. These findings are consistent with previous Raman and XANES pre-edge studies. Alkaline-earth-containing glasses behave somewhat differently, with Ti-[5] occurring in low TiO2 content glasses, becoming a mix of Ti-[4] and Ti-[5], and then gradually changing to predominantly Ti-[4] at higher TiO2 compositions. Finally, we have obtained data for a fresnoite composition (Ba2TiSi2O8) glass. Previous pre-edge and Raman data had suggested that this composition glass contained Ti-[5]; however, our Ti L-edge data indicate that Ti is almost exclusively Ti-[4], although some Ti-[5] may also be present.