However, the potential of precisely tailoring the anionic sublattice, e.g. by controlling the oxygen content or features of the oxygen defect structures, has been scarcely explored until now. In line with this concept and keeping in mind the increasing pressure to replace rare earths by other, non-critical, transition metals, we studied in a previous work the effect of the total substitution of lanthanum by barium in LaFeO3 system on CO oxidation performance Complete replacement of La by Ba, by a sol gel method, led to the stabilization of an oxide exhibiting hexagonal symmetry and oxygen vacancies with the composition BaFeO2.78. This phase crystallizes in a hexagonal (hcc)2-6H polytype, with a random distribution of anionic vacancies in both the hexagonal (h) and cubic layers (c).