Knowledge Bank

Raman spectra of vitreous silica specimens S1 and S2 stabilized at constant temperatures, $T(1)=1000\circ C$ and $T(2)=1300\circ C$, respectively, have been taken for Type III silica. In each spectrum, a narrow band centered around $600cm-1$, which is unmistakably characteristic of cristobalite and tridymite, is the more intense in specimens stabilized at the higher temperature while much broader bands around $400cm-1$ and $800cm-1$, to which quartz modes contribute strongly, are less intense in these specimens. The situation is reversed in both specimens stabilized at $1000\circ C$. These shifts in intensity were shown to be reversible in each of the specimens by inverting the stabilization temperatures and comparing the two spectra of the same specimen in each case. The stabilized glasses are assumed, therefore, to consist of mixtures of quartz and cristobalite + tridymite configurations in nearly equilibrium concentrations depending on the stabilizing temperature T(s) = T(1) or T(2). These observations and many others with respect to different properties reported in the literature support a general theory for glass-forming systems of which silica is a model.