Electrical properties of (Na2O)35.7(RE2O3)7.2(SiO2)57.1 (RE = Y, Sm, Gd, Dy, Ho, Er and Yb) glasses and ceramics

Fifteen kinds of sodium rare earth silicate glasses and ceramics with (Na2O)35.7(RE2O3)7.2(SiO2)57.1 (RE = Y, Sm, Gd, Dy, Ho, Er and Yb) composition were synthesized from a mixture of Na2CO3, RE2O3 and SiO2. The densities of the glasses were in fairly good agreement with the theoretical densities and were 0.2–0.41 g cm−3 larger than those of the polycrystalline ceramics. The conductivities of the glasses are 1–2 orders lower than those of the ceramics and the highest electrical conductivity was achieved for the Yb ceramic sample with the smallest ion radius of RE3+. The electromotive force, EMF, of the potentiometric CO2 gas sensors using (Na2O)35.7(Y2O3)7.2(SiO2)57.1 glass and ceramic increased linearly with an increase in the logarithm of CO2 partial pressure, in accordance with Nernst's law. It was suggested from the slope of Nernst's equation that the two electron-transfer reaction associated with the carbon dioxide molecule takes place at the detection electrode above 450 °C.