XPS investigations on coordination and valency of Ti in fresnoite glasses and glass ceramics

Abstract

Crystalline fresnoite (Ba 2TiSi 2O 8), attributed glasses and glass ceramics of the systems Ba 2TiSi 2O 8 + xSiO 2 ( x=0, 0.75) and Sr 2TiSi 2O 8 have been studied by X-ray photoelectron spectroscopy (XPS). To understand the process of crystallization, changes in coordination of the constituting elements have been studied in glassy and crystalline samples. It was observed that changes in coordination took place at the Ti-sites. It is shown that in fresnoite glass (Ba 2TiSi 2O 8), fivefold coordinated Ti predominates (≈60%) while fourfold (≈25%) and sixfold (≈15%) coordinated Ti is present as well. In another series of experiments, the effect of reducing Ti(IV) to Ti(III) by adding carbon to the glass batches was studied. It was shown that XPS could resolve the two valency states and gave Ti(IV)/Ti(III) ratios equal to that obtained from thermogravimetry. By comparison of all samples measured, XPS-line positions for different coordinations and valencies of Ti in these samples are given.