The stability of the Sr4Fe6O13phase, and the phase changes taking place in the presence of Co, are discussed. Reported transport parameters are analyzed and discussed in relation to defects and phase changes in SrFe1.5-xCoxOz. A defect model is suggested that is in qualitative agreement with the observed transport parameters. It is suggested that defect ordering due to Co2+ions is decisive for the transport properties.
Bredesen, R., & Norby, T. (2000). On phase relations, transport properties and defect structure in mixed conducting SrFe1.5-xCoxOz. Solid State Ionics, 129(1), 285–297. https://doi.org/10.1016/S0167-2738(99)00333-1