Systematic examination of hydrogen ion conduction in rare-earth doped barium cerate ceramics

Abstract

Protonic conduction is demonstrated in doped perovskites BaCe 1− x M x O 3−α ( M=Y, Yb, Nd, Gd, La; x=0.05, 0.10) at high temperature in a moist atmosphere. Conduction by protons was confirmed by EMF measurements on various gas cells using specimen ceramics as the solid electrolyte membrane separating moist and “dry” nitrogen atmospheres. Electrical conductivity (σ) measurements were carried out in the temperature range T=600–900°C using complex impedance techniques. A depressed semicircle in the impedance plane plots at T<700°C (and absent at higher temperatures) was assigned to interfacial (electrode/ electrolyte) charge transfer resistance. Plots of log (σ T) versus 1/ T showed Arrhenius behaviour in all cases. The highest electrical conductivities were those for Yb and Gd doped ceramics. It is postulated that water molecules react to fill vacant oxygen sites in the doped perovskites, thereby generating hydroxide ions (O o+V ∼ o+H 2O⇒2(OH) o), with the proton able to migrate between sites corresponding to attachment to adjacent oxygens.