Received 5 November 2010; revised 27 June 2011; Accepted 5 July 2011. Available online 12 July 2011.
In this paper, the ionic conductivities of La0.54Sr0.44Co0.2Fe0.8O3-δ and La0.6Sr0.4Co0.2Fe0.8O3-δ were measured by electron-blocked alternating current impedance analysis technique. The results show that the oxygen ion conductivity of La0.54Sr0.44Co0.2Fe0.8O3-δ is nearly five times higher than that of La0.6Sr0.4Co0.2Fe0.8O3-δ, which makes La0.54Sr0.44Co0.2Fe0.8O3-δ cathode more conductive than YSZ electrolyte. Consequently, the electrochemical reaction region is extended from the interface between the cathode and the electrolyte to the whole surface of the cathode grains, with a result of the cathode polarization overpotential being decreased and the cell electrical performance being improved. Besides, the XRD results show that both La0.54Sr0.44Co0.2Fe0.8O3-δ and La0.6Sr0.4Co0.2Fe0.8O3-δ begin to react with 8YSZ([Y2O3]0.08·[ZrO2]0.92) at 850 °C, but La0.54Sr0.44Co0.2Fe0.8O3-δ with a faster reaction rate. The thermal expansion experiments manifest that the two LSCFs have approximate thermal expansion coefficients, being about 14 × 10−6–15 × 10−6 K−1 from 500 °C to 700 °C, which is moderately higher than that of 8YSZ.