B-Site Doping and Oxygen Pressure

When B-site ions can take on a variety of oxidation states, a change in the external oxygen partial pressure can lead to an oxygen composition range for the brownmillerite phase. This additional oxygen has a number of structural consequences. The oxygen can occupy the vacancies in the brownmillerite phase and lead to new ordered phases, new coordination polyhedra such as trigonal prisms or square pyramids, discussed below (Section 2.5), or result in a disordered cubic perovskite phase. 

A similar disordering effect occurs when the brownmillerite structure oxide CaSrFej prepared in argon is heated in air, when it will oxidise to a com- 

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