Published online by Cambridge University Press: 21 February 2011
At high temperature, nonstoichiometric perovskite-type related ferrites can be oxidized in air. At first sight, this phenomenon appears rather surprising since it corresponds to a partial formation of iron +IV. Moreover a structural transition occurs from a vacancy ordering state to a pseudodisordering one characterized by a cubic perovskite-type X-ray diffraction pattern. A TEM study has shown in fact a more complex situation attributed to a microdomain texture. This is explained from a crystallographic point of view and correlated to the existence of mixed valencies of iron.