Creep behavior and its correlation with defect chemistry of La0.58Sr0.4Co0.2Fe0.8O3−δ

The creep behavior of La0.58Sr0.4Co0.2Fe0.8O3−δ (LSCF) perovskite was studied in the temperature range 750-950 °C in air and vacuum (PO2 ≈ 4 mbar). A transition in the apparent activation energy was found between 800 and 850 °C for both oxygen partial pressures. The apparent activation energy is ∼250 kJ mol−1 for the temperature range 700-800 °C under vacuum (PO2 ≈ 4 mbar) and ∼480 kJ mol−1 for 850-950 °C in both atmospheres. Above 850 °C, the creep rate of LSCF is higher in vacuum than in air although the same cubic structure exists. The stress exponent of the creep law is in the range 1.9-2.5 for all temperatures, which excludes a transition of creep mechanism. It is suggested that, below 800 °C, cation vacancies originate from the necessary balance with the substituted cations in LSCF, and the determined activation energy reflects the energy barrier for cation migration via these vacancies. Above 850 °C, additional vacancies appear to be formed intrinsically, and the activation energy represents the sum of the thermally activated formation energy of cation vacancies and migration energy of cations.