The effect of Ti4+ on the site of Al3+ in the structure of CaO–Al2O3–SiO2–TiO2 system glass

The structures of 20CaO · 17Al2O3 · 63SiO2, 20CaO · 17Al2O3 · 63SiO2 · 4.5TiO2, and 20CaO · 17Al2O3 · 63SiO2 · 9TiO2 glasses are investigated by the methods of 29Si-, and 27Al-MAS-NMR spectra, Al2p X-ray photoelectron spectroscopy and Raman spectra. The network of 20CaO · 17Al2O3 · 63SiO2 glass consists mainly of Q3 and Q4 groups and some Al3+ ions enter as the network formers in the form of [AlO4]Ca[AlO4] as well as [AlO4]CaO− and other Al3+ ions still stay as the network modifiers. When 4.5 mol.% TiO2 are added to this glass, the Ti4+ ions enter as the network formers in the form of [TiO4] and have no obvious effect on the site of Al3+. With 9 mol.% TiO2, the glass network consists mainly of Q2, Q3, and Q4 groups. The Ti4+ ions enter as the network formers and take the place of some Al3+ ions in the network, and some additional non-bridging oxygen ions corresponding to the above replaced Al3+ ions are formed, that introduces the Q2 groups and decreases the aggregation extent of glass network. This is also certificated by the differential thermal analysis (DTA).