Shcherbakov I. P., Narykova M. V., Chmel A. E.

Evolution of structural defects of SiO-=SUB=-2-=/SUB=--TiO-=SUB=-2-=/SUB=- glasses with a change in TiO-=SUB=-2-=/SUB=- concentration from zero to phase separation

The thermal expansion coefficient (TEC) of binary glasses SiO2-TiO2 decreases as the TiO2 concentration grows. At concentration of TiO2 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 TiO2 concentration from zero to phase separation. The precision measurements of density showed its drop at TiO2 content of 7.9 mol% thus evidencing the conversion of glass into a polycrystalline substance consisting of SiO2 and TiO2 crystallites. In the TiO2 concentration range of compatibility of oxides, an ensemble of point defects comprises =SiO-Si= and =Ti-O- centers as well as =Si-Si= and =Si-Ti= neutral oxygen-vacancies. At the dopant concentration specific for phase separation (TiO2 7.9 mol%), the PL-active groups of =Si-Ti= go away, while the IR-detectable Si-O-Ti bridges remain stable. Keywords: SiO2-TiO2 glass, point defects, structural defects, photoluminescence, IR spectroscopy.

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