Logarithmic kinetics of the amorphous-amorphous transformations in SiO2 and GeO2 glasses under high-pressure

We have studied in situ the kinetics of the amorphous-amorphous coordination transformation in GeO2 glass and of the initial stage of transformation in vitreous SiO2 up to 9 GPa by volume vs time measurements using the precise strain-gauge technique. The volume vs time dependence at all pressure points was found to obey the logarithmic law, which distinguishes the observed transformation kinetics from that of the ordinary transitions in crystals. The first evidence of anelastic behavior was found from the quasistatic equation of state at P approximate to 6-7 GPa for SiO2 glass and at 2-3 GPa for GeO2 glass, i.e., at lower pressures than previously believed.