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

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.