It was discovered that E′ centers were created by heat-treatment when silica glass contains water and had residual stress. Silica glass samples were heat-treated at 1000C for various lengths of time in 355torr water vapor pressure and dry N gas atmospheres. The electron paramagnetic resonance signal of E′ centers increased initially with heat-treatment time in both atmospheres but then decreased afterwards in the wet atmosphere. It was known that water molecules eliminate paramagnetic defects, such as E′ centers and non-bridging O hole centers by reacting with these defects in the glass, transforming them to non-paramagnetic species such as ≡Si–OH or ≡Si–H. The present study indicated that water molecules were also capable of initially creating paramagnetic defects in the glass structure by breaking the silica network structure in the presence of stress. The present observation may be relevant to mechanical strength reduction of silica glasses, which was commonly observed in the presence of water and stress.

Point Defect Formation and Annihilation in Silica Glass by Heat-Treatment - Role of Water and Stress. J.W.Lee, M.Tomozawa, R.K.MacCrone: Journal of Non-Crystalline Solids, 2008, 354[14], 1509-15