Alkali Ion Mobility in Mixed Cation Glasses (Part 2)

Abstract

The electrical conductivity of glasses in the system 2 R′2O⋅RO⋅7SiO2(R′: Li, Na, K, Cs; R: Be, Mg, Co, Sr, Ba, Zn, Pb) has been measured in the temperature range 350°-1200°C. Different effects of divalent cations on the electrical conductivity in a series of glasses containing a given alkali were observed in molten state (>Tg) and in solid state (<Tg). The electrical conductivity in molten state decreased with increasing difference in ionic radii between alkali and divalent cation, while the conductivity in solid state decreased monotonously with increasing ionic radius of the divalent cations. When a divalent cation is introduced into an alkali silicate glass, an alkali ion probably forms a pair with a divalent cation such as R′+…O…R2+ bond, giving weaker Coulombic repulsive force for the next nearest neighbor cations than in the R′+…O…R′+ bond and decreasing of the electrical conductivity. This effect appears only in molten state. However, in solid state, the mobility of alkali ions is considerably affected by frozen network structure depending on the transition temperature of these glasses, that is, the geometical factor for alkali migration and the electrical conductivity is reaponsible for the different from molten state. The explanation described above can be applied to the mixed alkali effects in glass also.