AbstractsChemistry

The responses of structure and properties to composition and temperature have been investigated for glasses in TiO2-SiO2 and Na2O-TiO2-SiO2 systems. Additionally, the response of Na2O-TiO2-SiO2 glasses to plastic deformation has been studied. (x)TiO2-(1-x)SiO2 glasses were prepared through the sol-gel process with compositions 0 ≤ x ≤ 10 mol% and compared to commercial glasses prepared through flame hydrolysis deposition with x = 0, 5.4, and 8.3 mol%. (x) Na2O - (y) TiO 2 - (1-x-y) SiO2 glasses were prepared with x = 10, 15, 20, and 25 mol% and y = 4, 7, and 10 mol% through a melt-quench process. Density and index of refraction of glasses was measured through the Archimedes's method and using a prism coupler, respectively. The glass transition temperature of Na2O-TiO2-SiO2 glasses was measured through differential thermal analysis. The structure and elastic moduli have been studied through Raman spectroscopy and Brillouin light scattering, respectively, at room temperature and in-situ up to 1200 °C for TiO2-SiO2 glasses and up to 800 °C for Na2O-TiO2-SiO2 glasses. Young's modulus was observed to decrease from 72 GPa to 66 GPa with the addition of 8.3 mol% TiO2 in TiO2-SiO2 glasses and to increase from 65 GPa to 73 GPa with the addition of 10 mol% TiO2 in 10 Na2O - (0-10) TiO2-SiO2 glasses. The addition of TiO2 was observed to shift the 460, 490, and 600 cm-1 Raman peaks to lower frequencies in TiO2-SiO2 glasses, suggesting a more open and flexible network, and the 720, 800, and 840 cm -1 Raman peaks to higher frequencies in Na2O-TiO2 -SiO2 glasses, suggesting a lower free volume and stiffer network. The addition of TiO2 has little effect on the temperature response of the elastic moduli in either system, but decreases the thermal expansion and increases the frequency shifts in the 950 and 1100 cm -1 Raman peaks in the TiO2-SiO2 system while the thermal expansion increases with initial additions of TiO2 and then remains constant in the Na2O-TiO2-SiO 2 system. Changes in structure and property with composition have been discussed, and structural models were proposed. The reduction of thermal expansion and elastic moduli in TiO2-SiO2 glasses occurs through the promotion of cooperative, inter-tetrahedral rotations facilitated by the longer and weaker Ti-O bonds. The increase in elastic moduli in the Na2O-TiO 2-SiO2 glasses occurs through the formation of small clusters with local, relatively high Ti and Na concentrations, promoted by Ti adopting a five-fold…