Conduction of Sodium and Nonbridging Oxygen Ions in Sodium Silicate Glass

Abstract

From thermally-stimulated polarization/depolarization current studies of bulk glasses of Na2O–2SiO2 and Na2O–3SiO2, the following conclusions were made. First, the great reduction of dc conductivity down to a few hundredths with decreasing sample thickness is explained in terms of the presence of inherent microheterogeneity in the glass structure. Second, the peak which previously was assigned generally as due to localized motion of nonbridging oxygen ions in the alkali-depleted region near the anode is better assigned as due to conduction polarization of those ions. Then the activation energy for conduction of nonbridging oxygen ions is estimated to be roughly 6±2 kcal/mole more than that for alkali conduction. And third, because of the high conductivity of bulk samples, degradation of alkali conduction by space charges accumulating near the electrodes during polarization generates the peak at around 10-8–10-7 Ω-1 cm-1.