Effects of aluminum impurity on the structural relaxation in silica glass

To elucidate effects of Al impurity on the glass-forming process in silica glass, the structural relaxation in Al-containing silica glass, with alkali ions of only trace levels, was investigated by observing the fictive temperature. The fictive temperature was determined by infrared (IR) absorption analysis. Al, even at concentrations lower than 10 wtppm, increases the relaxation time and the activation energy of the α-relaxation. It also suppresses the sub-relaxational process due to OH ions. These results indicated that Al should have other effects on structural relaxation than alkali–aluminate complex formation, as has been thought to be the cause for an increase in the α-relaxation time and thus the viscosity of silica glass. Furthermore, the structural relaxation does not merely depend on the number of non-bridging oxygen atoms in the glass network.