**3. Results**

#### **3.1 Characterization of Ln1−xAxFeO3−δ (Ln=La, Nd, Pr; A=Sr, Ca) perovskites with 0.2≤x≤0.8**

The (La**1−x**Sr**x**)FeO3- (LSF) perovskite system exhibits high electronic and oxide ion conductivities at high temperatures, which make it attractive for solid oxide fuel cell (SOFC) cathodes. Several works (Ecija et al., 2011; Rodríguez-Martínez & Attfield, 1996; Vidal et al., 2007 and references therein) have shown that the physical properties of these perovskite materials are very sensitive to changes in the doping level (x) the average size of the A cations (<rA>) and the effects of A cation size disorder (2(rA)).

The synthesis of these compounds allows us to study the effect of the variation of the doping level x on the properties of the perovskites with general formula Ln1−xAxFeO3−δ (Ln=La, Nd, Pr; A=Sr, Ca) applied as SOFC cathodes. This has been achieved by keeping constant both the average size (<rA>) and the size mismatch (2(rA)) to 1.22 Å and 0.003 Å2, respectively.

For the preparation of this series the solid state reaction route has been chosen due to its simplicity to obtain perovskite phases in the same synthetic conditions.
