Investigation of metal-induced low-temperature crystallization of SiO2 sol-gel glass containing Ag

The transition of the Ag-doped amorphous SiO2 sol-gel made bulk samples into the crystalline alpha -crystobalite has been observed during the heat treatment at temperature of 500 degreesC, which is much lower than the values reported earlier. For that, silver has to be added to the starting solution in an amount such that it forms aggregates at the heat treatment. The other requirement to observe the metal- induced low-temperature crystallization is that the composition of the starting solution (namely, the water-to-TEOS ratio) ought to correspond to some optimal values resulting in the samples with the isotropic glass structure. Two possible mechanisms of the effect are discussed, one takes into account the electrostatic screening of the ion's charge by the metal particle surface, and the other considering the interaction of the metal atom with the interatomic bonds of the glass during the diffusion of the atom through the glass. It is shown that both effects lead to the local sample's heating which could be the reason for the crystallization observed.