Formation of TiO2 Nanocrystallites in the TiO2-ZnO-B2O3-Al2O3 Glass-Ceramics

We have examined the structure and the crystallization behavior of the 13TiO2xZnO17Al2O3(70-x)B2O3 (TZAB) glass. Coordination number of B2O3 and Al2O3 is changed by substitution of B2O3ZnO, whereas coordination states of TiO2 and ZnO are not affected by the substitution. With increasing amount of ZnO, network forming AlO4 increases instead of network modifying AlO5 and AlO6. In the case of B2O3, BO4 unit is preferentially formed with increasing amount of ZnO. The glass-ceramics show selective crystallization of TiO2, and the precipitated phase of TiO2 depends on the amount of ZnO. Dendritic-like aggregates of anatase crystallites were precipitated in the glass-ceramic containing lower amount of ZnO, whereas isolated granules of rutile crystallites were precipitated in the glass-ceramic containing higher amount of ZnO. We have demonstrated that the transparency of the glass-ceramic strongly depends on the crystallinity of precipitated crystallites. The crystallization behavior indicates that both main network and the interstitial components were affected by the substitution.