Titanium environment in TiO2-BaO-ZnO-B2O3 glasses by x-ray absorption spectroscopy

The local environment of titanium in glasses of the system TiO2-BaO-ZnO-B2O 3 was studied by x-ray absorption spectroscopy. In all glasses, for TiO2 co ntent varying from 35 to 49 mol%, the titanium atoms are mainly fourfold co ordinated network formers. For the glass with the highest titanium content, about 20% of the titanium enters into a sixfold environment, indicating th e presence of precrystalline nuclei. These nuclei are responsible for the d ecrease of the optical performance of the glass above threshold titanium co ntent, prior to any observable crystallization.