Proton conduction and chemical stability of (La 0.5Sr 0.5)(Mg 0.5+ yNb 0.5− y)O 3− δ

Abstract

Electrical conduction properties of complex perovskite-type oxides in the (La 0.5Sr 0.5)(Mg 0.5+ y Nb 0.5− y )O 3− δ ( y = 0.02–0.06) series at intermediate-high temperatures were investigated; introduction of protons by hydration of oxide-ion vacancies was expected by increasing the Mg/Nb ratio from unity. The conductivity depended on y and a maximum conductivity was obtained at y = 0.04: σ = 4.9 × 10 −6 S cm −1 at 400 °C in wet H 2 atmospheres. From electromotive force measurements of hydrogen and water vapor concentration cells, electrical conduction in wet H 2 atmospheres can be attributed to ionic conduction, and proton conduction is dominant below 700 °C. Unlike other perovskite-type proton conductors, (La 0.5Sr 0.5)(Mg 0.54Nb 0.46)O 3− δ was stable in CO 2 atmospheres even in the low-intermediate temperature region due to dilution of reactive strontium by lanthanum.