Oxygen Transport and Nonstoichiometry in SrFeO_3-δ

Abstract

Chemical diffusion () and surface exchange (k) coefficients for SrFeO_3-δ were measured using an electrochemical cell combined with electrochemical impedance spectroscopy (EIS) and potential step technique (PS) in the temperature range of 850-915°C. A value of ~ 4·10^-5 cm²/s and a k value of ~ 8·10^-5 cm/s were obtained at 900°C. Slow scan (0.5-3 μV/s) cyclic voltametry (CV) was performed in the same temperature range and using the same electrochemical cell to obtain oxygen nonstoichiometry data. The oxygen nonstoichiometry (δ) at 900°C in air was determined as 0.4. A plateau corresponding to δ = 0.5 was observed below an oxygen partial pressure (p (O₂)) of 10^-6 atm. These results were shown to be consistent with the literature data. Nonstoichiometry data were further analysed using the existing defect models, and the limits of the independent point defect approximation and the necessity of considering interactions between point defects and clusters were established.