Possible Evidence of a Point of Discontinuity (T*) on the Arrhenius Relationship for the Ba_0.5Sr_0.5Co_1-xFe_xO_3-δ Solid Solutions: A Non-Conventional Analysis

Ba_0.5Sr_0.5Co_1-xFe_xO_3-δ solid solutions (x = 0.2, 0.5 and 0.8) have been studied by means of electrochemical impedance spectroscopy (EIS) in the temperature range of 500-800 °C under different atmospheres (oxygen and air). EIS measurements of oxygen reduction reaction (ORR) show a possible non-Arrhenius behavior at T*=680 ^oC. Moreover, this paper reviews the experimental evidence of a non-Arrhenius behavior (curvature) instead of a linear extrapolation commonly used in literature. Non-Arrhenius behavior is ascribed to a chemical step (Warburg-type impedance element) at a low-frequency range when the temperature is below T*. An electrochemical model is also tentatively proposed to explain the non-Arrhenius behavior of Ba_0.5Sr_0.5Co_1-xFe_xO_3-δ at T*=680 ^oC.