Annealed samples from a single melt of this glass were re-heated to temperatures ranging from 450 to 800C, held isothermally (1200s), and quenched in air or silicone oil. The complex impedances of the annealed and quenched samples were then measured as a function of temperature (120 to 250C) using alternating-current (1Hz to 1MHz) impedance spectroscopy. The direct-current conductivity was deduced from the low-frequency intercepts of semicircular fits to the complex impedance data. It was found that, when the direct-current conductivity at 150C was plotted against the soaking temperature, the results fell into 3 main regions. These were explained in terms of the structural relaxation time of the glass. The direct-current conductivity was also measured for various soaking times at 550C. From these data, an average relaxation time of 438s was calculated.

P.W.Angel, M.R.De Guire, A.R.Cooper: Journal of Non-Crystalline Solids, 1996, 203, 286-92