Proton conduction and chemical stability of (La0.5Sr0.5)(Mg0.5+yNb0.5−y)O3−δ

Abstract Electrical conduction properties of complex perovskite-type oxides in the (La 0.5 Sr 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 0.5 Sr 0.5 )(Mg 0.54 Nb 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.