Characterization of Ln0.5M0.5FeO3–δ (Ln = La, Nd, Sm; M = Ba, Sr) perovskites as SOFC cathodes

Ln0.5M0.5FeO3–δ (Ln = La, Nd, Sm; M = Ba, Sr) perovskites have been synthesised by the glycine-nitrate route in order to obtain compounds with good morphological and electrical characteristics to be used as SOFC cathodes. A systematic study of the influence of the average ionic radius of the A cation (<rA>), on the structural, morphological and electrical properties of these perovskites has been performed. The obtained materials have been characterised by ICP-AES analysis, X-ray powder and neutron powder diffraction, scanning electron microscopy and four-probe conductivity measurements. In this study <rA> has been changed in the range 1.34 ≥ <rA > ≥ 1.25 Å, while keeping constant the doping level, x = 0.5 (in A position) and A cation size disorder, σ2 (rA) = 0.0161 Å2. Overall, the sample with the higher average ionic radius showed the highest values of conductivity. Chemical compatibility of the proposed cathodes with yttria-stabilised zirconia electrolyte (YSZ) has also been analysed. The data indicate that additional phase formations exist in all systems at temperatures above ~ 1000 °C.