The Structure of SiO2-Sol-Gel Glasses Produced from Gels with Various Mole-Water per Mole-TEOS Ratios

ABSTRACTSiO2-gels produced with 4,8, and 16 mol water per mol TEOS were densified up to 1000°C and then exposed to gamma-ray irradiation in order to produce paramagnetic defect centers. Various paramagnetic states were detected during densification of these gels, the formation of which depends on the mol water per mol TEOS ratio. In the gels O−2 ions were detected. The paramagnetic centers detected in the n = 16 gel with TH = 900°C were attributed to a non-bridging oxygen and an E'1-center. Three different O−2 ions, probably in interstitial positions, were detected in the n = 16-gel with TH = 1000°C. The CO−2 center was observed in the n = 8 gel with TH = 900°C. A variety of new components occur at TH = 1000°C in the n = 8 gel, the origin of which remains unresolved at present. The CH3, CO−2, and E1′-centers were detected in the n = 4 gel with TH = 700°C. The CO−2 and E′1 centers were preserved after heat treating the n = 4 gel at TH = 1000°C.