Figure 1

(Color online) (a) Uncorrected, room-temperature Raman spectrum of potassium disilicate glass ($33.3\mathrm{mol}\%$ ${\mathrm{K}}_2\mathrm{O}$). The background was determined by fitting a second order polynomial to the spectral region between 1250 and $1800{\mathrm{cm}}^{-1}$, where no Raman signal is present; (b) background corrected spectrum; (c) temperature-frequency corrected spectrum.Reuse & Permissions

Figure 2

(Color online) Raman intensity as a function of Raman shift and temperature for a fast quenched, $33.3\mathrm{mol}\%$ ${\mathrm{K}}_2\mathrm{O}$ sample: (a) three-dimensional plot, (b) intensity map, and (c) individual spectra for different temperatures. Raman spectra were collected at $\sim 15\mathrm{K}$ intervals, with an overall heating rate of $\sim 10\mathrm{K}∕\min$. The intensity of the band at $\sim 925{\mathrm{cm}}^{-1}$ is fairly constant below the glass transition range $(\sim 720–800\mathrm{K})$, decreases on approaching the glass transition, and increases above the glass transition. The decrease in intensity upon approaching the glass transition results from the slow heating rate compared to the quench rate. In other words, during the slow heating, sufficient time was available for the structure to relax toward its equilibrium state.Reuse & Permissions

Figure 3

(Color online) (a) Peak maxima for the $\sim 925{\mathrm{cm}}^{-1}$ region as a function of temperature during constant rate heating $(0.14\mathrm{K}∕\mathrm{s})$. (b) Fictive temperature as a function of the actual temperature; $T_f$ is obtained by projecting the data in Fig. 3a along the sub-$T_g$ slope onto the fit through the point at equilibrium. The cooling and heating curves that are calculated from the viscosity data for the respective quench and heating rates are also plotted.Reuse & Permissions

Figure 4

(Color online) Peak maxima for the $\sim 925{\mathrm{cm}}^{-1}$ region as a function of time after a fast temperature step from below $T_g$ into the glass transition range: (a) from $575\text{to}703\mathrm{K}$ and (b) from $592\text{to}712\mathrm{K}$; points mark the data; the line is an exponential fit through the data $(y=y_0+a{e}^{-x∕t})$; the corresponding relaxation times $t$ are marked in the figure. As expected, relaxation is slower at $703\mathrm{K}$ than at $712\mathrm{K}$.Reuse & Permissions

Figure 5

${\log }_{10}\eta$ as a function of temperature for potassium silicate melts (Ref. 32, 33, 34). The values obtained from the structural relaxation observed in the Raman spectra $(33.3\mathrm{mol}\%)$ are also plotted.Reuse & Permissions

Figure 6

(Color online) (a) Selected Raman spectra for the $450–700{\mathrm{cm}}^{-1}$ spectral region. The arrow indicates the peak assigned to three-membered rings. (b) Fictive temperature as a function of the actual temperature for glasses prepared with different quench rates. The fictive temperatures have been obtained from the intensity of the peak assigned to three-membered rings.Reuse & Permissions