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

The structures of 20CaO . 17Al(2)O(3). 63SiO(2), 20CaO . 17Al(2)O(3). 63SiO(2). 4.5TiO(2), and 20CaO . 17Al(2)O(3). 63SiO(2). 9TiO(2) glasses are investigated by the methods of Si-29-, and Al-27-MAS-NMR spectra, A12p X-ray photoelectron spectroscopy and Raman spectra. The network of 20CaO . 17Al(2)O(3). 63SiO(2) glass consists mainly of Q(3) and Q(4) 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 Q(2), Q(3), and Q(4) 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 Q(2) groups and decreases the aggregation extent of glass network. This is also certificated by the differential thermal analysis (DTA). (C) 1998 Elsevier Science S.A. All rights reserved.