Structural relaxation in AgPO3 glass followed by in situ ionic conductivity measurements

The structural relaxation kinetics of a silver meta-phosphate glass (AgPO3) is investigated using a method based on the isothermal variation of its ionic conductivity over time. Samples of AgPO3 glass from the same batch were pre-annealed at 433 K or 418 K and then relaxed at different temperatures within this temperature range, which is close to its glass transition temperature measured by differential scanning calorimetry, T-g(DSC) = 438 K. Ionic conductivity data were continuously collected by impedance spectroscopy during the isothermal relaxation process. The variation of the electrical conductivity over time is well described by the Kohlrausch expression (Phi(t) = exp[ - (t/tau(kappa)(sigma))beta]), in which tau(kappa)(sigma) is the characteristic relaxation time and beta a stretch exponent. Different values of beta were found when the glass structure expanded or contracted during relaxation. In addition, viscosity values calculated by the Maxwell relationship using <tau> from conductivity data and a shear modulus taken from the literature are in accordance with the experimental viscosity measured in the same temperature range, thus validating the use of ionic conductivity to unveil glass structural relaxation. (C) 2016 Elsevier B.V. All rights reserved.