Electrical properties of (Na₂O)_35.7(RE₂ O₃)_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 Na₂ CO₃, 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 (Na₂ O)_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.