Oxygen transport and nonstoichiometry in SrFeO3-δ

Chemical diffusion ((D) over tilde) and surface exchange (k) coefficients for SrFeO3-delta were measured using an electrochemical cell combined with electrochemical impedance spectroscopy (EIS) and potential step technique (PS) in the temperature range of 850-915 degrees C. A (D) over tilde value of similar to 4.10(-5) cm(2)/s and a k value of similar to 8.10(-5) cm/s were obtained at 900 degrees C. Slow scan (0.5-3 mu V/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 (delta) at 900 degrees C in air was determined as 0.4. A plateau corresponding to delta = 0.5 was observed below an oxygen partial pressure (P(O-2)) of 10(-5) 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 pc,int defect approximation and the necessity of con sidering interactions between point defects and clusters were established.