Investigation of the Role of Nucleating Agents in MgO-SiO2-Al2O3-SiO2-TiO2 Glasses and Glass-Ceramics: A XANES Study at the Ti K- and L2,3-Edges

International audience; We report a X-ray absorption study at Ti K- and L2,3-edges to determine the role of TiO2 content as a nucleating agent in glass ceramics. It is found that the local Ti environment is not modified with TiO2 addition, indicating that medium range organization is responsible for its ability to promote internal versus bulk nucleation. We have identified a Ti coordination change between the nucleation front and the crystallized part of the glass ceramic. These changes correspond to conversion from 5-fold coordinated to 4-fold coordinated Ti in the remaining glassy part, resulting from compositional changes. This reveals that active sites for nucleation could be experimentally detected and that reorganization of the glass matrix during nucleation has a major influence on the ongoing nucleation processes.