High-temperature electrical conductivity and electrochemical activity in oxygen redox reaction of La-doped Sr2FeCo0.5Mo0.5O6-δ

High-temperature electrical conductivity and electrochemical activity in the oxygen redox reaction of Sr2FeCo0.5Mo0.5O6-δ (SFCM) and Sr1.6La0.4FeCo0.5Mo0.5O6-δ (LSFCM) at variable oxygen partial pressure have been studied. We have found that the partial replacement of Sr2+ by La3+ results in a substantial decrease in the total electrical conductivity due to a decrease in the hole charge carrier concentration. Detailed analysis of the high- and low-frequency parts of the impedance spectra at pO2 = 0.1–1 atm and 873–1173 K has revealed different rate-limiting steps in the oxygen redox reaction for SFCM and LSFCM resulted from different oxygen vacancy concentrations in these materials. For SFCM, the oxygen redox reaction is limited by the processes of adsorption and dissociation of oxygen molecules, while for LSFCM by the charge transfer occurring at the triple phase boundary.