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

Abstract

The transition of the Ag-doped amorphous Si02 sol-gel made bulk samples into the crystalline a-crystobalite has been observed during the heat treatment at temperature of 500 "C, which is much lower than the values reported earlier. For that, silver has to be added to the starling solution in an amount such that it forms aggregates at the heat treatment. The other requirement to observe the metalinduced low-temperature crystallization is that the composition of the starting solution (namely, the water-to-TEOS ratio) ought to correspond to sonie optinial values resulting in the samples with the isotropic glass structure. Two possible mechanisms of the eflect are discussed, one takes into account the electrostatic screening of the ion's charge by the metal particle siirjace, and the other considering the interaction of the metal atoni with the interatomic bonds of the glass during the difliision of the atom through the glass. It is shown that both effects lead to the local saniple's heating which could be the reason for the crystallization observed