To get information about the redox process in hexagonal BaFeO2.96, the temperature for the electron microscopy experiment was optimized to 300 ºC to prevent an irreversible transition to a non-hexagonal type-phase. At 300 ºC, the presence of extra superstructure maxima along the (010)* and (110)* and equivalent reciprocal 6H directions is observed (see Figures ), suggesting that the sample is reduced and the oxygen vacancies accommodate in the ab plane of the structure, as previously described for the BaFeO2.78 composition . The analysis of the contrasts of the HR-TEM images recorded along