Abstract:
The thermal expansion coefficient (TEC) of binary glasses SiO$_2$–TiO$_2$ decreases as the TiO$_2$ concentration grows. At concentration of TiO$_2$ in the range of 4–6 mol% (in dependence of the applied synthesis method) TEC becomes negative; at concentration of 8–11 mol% devitrification occurs. A combination of photoluminescence (PL) and IR reflection techniques were applied for studying the evolution of point and structural defects in the range of TiO$_2$ concentration from zero to phase separation. The precision measurements of density showed its drop at TiO$_2$ content of 7.9 mol% thus evidencing the conversion of glass into a polycrystalline substance consisting of SiO$_2$ and TiO$_2$ crystallites. In the TiO$_2$ concentration range of compatibility of oxides, an ensemble of point defects comprises $\equiv$SiO–Si$\equiv$ and $\equiv$Ti–O$^-$ centers as well as $\equiv$Si–Si$\equiv$ and $\equiv$Si–Ti$\equiv$ neutral oxygen-vacancies. At the dopant concentration specific for phase separation (TiO$_2$ 7.9 mol%), the PL-active groups of $\equiv$Si–Ti$\equiv$ go away, while the IR-detectable Si–O–Ti bridges remain stable.
Keywords:SiO$_2$–TiO$_2$ glass, point defects, structural defects, photoluminescence, IR spectroscopy.
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