Generic α relaxation in a strong ${\mathrm{GeO}}_2$ glass melt

The viscoelastic $\alpha$ relaxation in glass-forming ${\mathrm{GeO}}_2$ was measured over a range of temperatures near the glass transition using photon correlation spectroscopy. The relaxation in this “strong” glass former exhibits a nonexponential decay identical to that found in a great many simple organic “fragile” liquids. This finding contradicts the longstanding conjecture that nonexponentiality of viscous relaxations near the glass transition are correlated to the liquid's fragility. Instead, the findings offer support for a recent proposal that the nonexponentiality parameter of the $\alpha$-relaxation in supercooled liquids displays a universal value $\beta \left(T_g\right)=1/2$ near the glass transition.

Figure 1

Intensity autocorrelation functions obtained from ${\mathrm{GeO}}_2$ at selected temperatures shown. Solid lines are fits to Eq. (3) and the dashed line is an exponential decay shown for comparison. (Inset) A plot of the curve fitted residuals for the autocorrelation collected at $729{}^{\circ }\mathrm{C}$ shows deviations between data and fit are less than 1%.

Figure 2

The average relaxation time for the $\alpha$-relaxation in ${\mathrm{GeO}}_2$ as a function of inverse temperature. (Inset) The stretching exponent also as a function of inverse temperature.

Figure 3

Plot of the stretching exponents reported for four major oxide glasses [10, 24, 29] as a function of inverse temperature scaled to the individual glass transition temperatures. The dashed line is linear fit discussed in the text that extrapolates to $\beta \left(T_g\right)=0.52$.