X-ray absorption spectroscopy investigation of Ba2TiSi2O8+xSiO2 glasses

The local order in the vicinity of Ti and Ba atoms in Ba2TiSi2O8+xSiO2 (x=0.0, 0.1, 0.5 and 0.75) glasses was studied by X-Ray absorption Spectroscopy (XAS). The coordination number of Ti4+ atoms was identified by using the fingerprint X-Ray absorption near-edge structure (XANES) spectra of well-defined crystalline references. Coordination numbers 4, 5 and 6 could be observed in the glass. With increasing the amount of SiO2, the Ti4+ coordination number shifts to higher values. The coordination of Ba2+ atoms is not influenced by the composition of the glass. This may result from the large coordination number of this ion. The behavior of Ti as a network former or a network modifier depends on the coordination number. Additionally, the coordination number of Ti depends on the relation between network former and network modifier in the glass.