Investigation of metal-induced low-temperature crystallization of SiO/sub 2/ sol-gel glass containing Ag

Abstract

The transition of the Ag-doped amorphous SiO/sub 2/ sol-gel produced bulk samples into the crystalline /spl alpha/-crystobalite has been observed during heat treatment at a temperature of 500/spl deg/C, 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 on 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 samples with an 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 local sample heating which could be the reason for the crystallization observed.