(La_0.8Sr_0.2)(Mn_1-yFe_y)O_3±δ oxides for ITSOFC cathode materials? Electrical and ionic transport properties

International audienceThe oxygen transport properties in (La0.8Sr0.2)(Mn1-yFey)O3±δ (LSMF) with various iron contents y = 0, 0.2, 0.5, 0.8 and 1 were determined by the IEDP technique. Both oxygen diffusion and surface exchange coefficients were found to be greater for y = 0.8 and 1 than those of LSM (y = 0). Moreover, for y ≤ 0.5, grain boundary diffusion was the rate limiting step especially at lower temperatures. Thus, in the LSMF perovskite materials, the oxygen diffusion via oxygen vacancies is enhanced by Fe. The LSMF electrical performances were measured by impedance spectroscopy. Compared to LSM and LSF (y = 1), porous LSMF cathodes with y = 0.2–0.8 exhibit poor electronic conductivity: Fe, by reducing the number of couples Mn3+/Mn4+, decreases the amount of available hopping sites, limiting the electrical conduction. For LSF, the charge disproportionation Fe3+/Fe5+ improves the electrical properties. In conclusion, only the LSMF compounds with y~1 or 0 can be considered as good cathode materials for SOFC application