Proton conduction in non-perovskite-type oxides at elevated temperatures

Abstract

Ionic conduction in two non-perovskite-oxides, fluorite-related-type lanthanum tungsten oxide and aragonite-structure lanthanum borate, was investigated at elevated temperatures. La x WO 3+1.5 x ( x≅6) with a fluorite-related structure showed protonic conduction under hydrogen-containing atmospheres. The emf of a hydrogen concentration cell showed that the ionic transport number in hydrogen was about 0.7–0.9. The result of an electrochemical hydrogen pumping experiment using La x WO 3+1.5 x directly evidenced the protonic conduction in this oxide. Partial substitution of Zr for La lowered the electrical conductivity, while the influence of Nd substitution was small. The electrical conductivity of the aragonite-type oxide salt LaBO 3 increased by doping with Sr, although the conductivities of these ceramics were not high. The emf values of a hydrogen concentration cell using lanthanum borate (LaBO 3) were stable and close to theoretical values, suggesting that electrical conduction in this oxide was due to protons.