Structure of heat-treated sol-gel SiO₂ glasses containing silver

The crystallization of bulk amorphous SiO₂ samples, prepared by the sol-gel method, was obtained by heat treatments in air at temperatures as low as 500 °C. This occurs when silver is added to the precursor solutions in an amount such that it forms aggregates embedded in the glass. Another requirement to observe the low-temperature glass crystallization is that the bulk samples must be prepared from precursor solutions with specific compositions. These compositions, have a high H₂O/TEOS ratio, which produces an amorphous SiO₂ structure with some structural similarities to cristobalite, the phase in which the SiO₂ glass crystallizes.