Raman study of TiO2 role in SiO2-Al2O3-MgO-TiO2-ZnO glass crystallization

The starting glasses were found in almost complete disorder, since all bands were weak, broad and dominated by a Bose band at about 90 cm−1. After the sample annealing all bands turned out better resolved and the Bose band practically disappeared, both confirming the amorphous structure reorganization process. A multiplet observed in the vicinity of 150 cm−1 we assigned to the anatase and other titania structures that can be considered prime centers of crystallization. Finally, in the closest neighborhood of the Rayleigh line the low frequency mode characterizing nanoparticles was observed. According to this band theory, the mean size of initial titania crystallites is about 10 nm for all samples, but the size distribution varies within factor two among them.