Effect of cobalt substitution on thermal stability and electrical conductivity of Sm0.95Ce0.05FeO3 − δ in oxidizing and reducing conditions

A series of cobalt doped Sm0.95Ce0.05FeO3 − δ perovskites with formula Sm0.95Ce0.05Fe1 − xCoxO3 − δ (x = 0–0.10) were prepared by thermal decomposition of amorphous citrate precursors followed by calcination at 850 °C in air for 24 h. These materials are stable in air even at 1350 °C and under reducing conditions (5% v/v H2/N2) up to ∼ 800 °C, when phase separation ensues. Their conductivities were measured both in air and H2/N2 by the four point probe method from 25 °C to 1000 °C. The electrical conductivities increased from x = 0 to x = 0.10 in air with an increase in both temperature and cobalt concentration but in H2/N2 the trend is non-linear. The higher conductivity in air is due to oxygen vacancies created as a result of cobalt doping. Improved conductivity of Sm0.95Ce0.05Fe1 − xCoxO3 − δ in 5%v/v H2/N2 as compared to air is as high as two orders of magnitude. The specific species responsible for the sensing behavior (conductivity changes) is unclear, but the surface analysis by XPS showed that all these materials have a samarium rich surface. The potential sensing ability of these materials toward reducing atmospheres was probed with variable concentrations of H2/N2 gas. A linear and reversible response was observed with high sensitivity at room temperature.