Effect of the A Cation Size Disorder on the Properties of an Iron Perovskite Series for Their Use as Cathodes for SOFCs

In order to develop a cathode that can be used in intermediate temperature solid oxide fuel cells, a family of iron perovskites with the general formula Ln 0.5 M 0.5 FeO 3–δ (A = Ln 1– x M x ; Ln = La, Nd and/or Pr; M = Sr, Ca or/and Ba) with fixed divalent dopant concentration x to 0.5, mean A cation radius 〈 r A 〉 to 1.25 Å but with different A cation size disorder σ 2 ( r A ) has been prepared by the conventional solid state reaction. These compounds have been characterised by power X‐ray diffraction (XRD), high‐resolution scanning electron microscopy (SEM), electrical conductivity, I – V measurements and AC impedance spectroscopy. All the samples have a rhombohedral crystal structure (space group: R‐ 3 c ). SEM images show that the average grain size increases with increasing σ 2 ( r A ) in the bulk samples. The DC four‐probe measurements indicate that electrical conductivity is strongly dependent on the σ 2 ( r A ). Electrochemical impedance spectra at 700 and 800 °C revealed that better electrochemical cathode performances are for samples with smaller values of σ 2 ( r A ).