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

Electrical conduction properties of complex perovskite-type oxides in the (La0.5Sr0.5)(Mg0.5+yNb0.5−y)O3−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 H2 atmospheres. From electromotive force measurements of hydrogen and water vapor concentration cells, electrical conduction in wet H2 atmospheres can be attributed to ionic conduction, and proton conduction is dominant below 700 °C. Unlike other perovskite-type proton conductors, (La0.5Sr0.5)(Mg0.54Nb0.46)O3−δ was stable in CO2 atmospheres even in the low-intermediate temperature region due to dilution of reactive strontium by lanthanum.