Following previous work on silicate doping of perovskite (Sr/Ca)MnO3 and (Sr/Ca)FeO3-δ materials for potential application as electrode materials for solid oxide fuel cells, here we report the successful incorporation of silicon into the mixed Mn/Fe systems, (Sr/Ca)2MnFeO6-δ. The results show a higher level of Si doping to be possible for Ca2MnFe1-xSixO6—δ (0≤x≤0.4) compared to Sr2MnFe1-xSixO6—δ (0≤x≤0.2). In both cases, the conductivity is improved for low doping levels (x≤0.1), with a subsequent decrease for higher doping levels. Additional preliminary work has shown that phosphate can also be successfully incorporated into these perovskite systems. The work therefore further illustrates the potential of oxyanion doping in perovskite systems of interest for Fuel Cell applications.