Relations between composition, temperature and electrical conductivity of (60-x)SiO2-40Na2O-xCaO(x= 0~15 wt%) glass system

Abstract

We report the electrical conductivity of the mixed alkali silicate glasses in the system (60-x)<TEX>$SiO_2-40Na_2O-xCaO(x=0\sim15wt%)$</TEX> in the temperature range from <TEX>$150^{\circ}C$</TEX> to <TEX>$620^{\circ}C$</TEX>. In the range from <TEX>$150^{\circ}C$</TEX> to glass transition temperature<TEX>$(T_g)$</TEX>, the electrical conductivities of glass samples had a tendency to be proportion with temperature. The glasses of containing over 7.5wt% CaO showed lower conductivities than the glasses of containing 0 and 5wt% CaO because two kinds of alkali ions<TEX>$(Na^+,\;Ca^{2+})$</TEX> were obstructed each other. On the other hand, in the range from <TEX>$T_g$</TEX> to <TEX>$620^{\circ}C$</TEX>, the electrical conductivity of glasses(<TEX>$7.5{\leq}x{\leq}12.5$</TEX>) was unstable and decreased in some region. From XRD results, the <TEX>$Na_4Ca(SiO_3)_3$</TEX> phase were observed in these glasses. This means the alkali ions didn't behave as carrier, it seems that this caused the conductivities decrease. In case of glass of containing 15wt% CaO, any crystal phase were not observed. This means the alkali ions behaved as carrier, it consequently seems the conductivity increased.