Investigating the controlled oxidation of manganese oxides with the Brownmillerite structure

Brownmillerite structures have received much attention due to their defect perovskite structure and potential for interesting magnetic behaviour and ionic conductivity. This thesis describes an initial investigation into the potential of manganese containing Brownmillerite phases, with the stoichiometry (Sr2-xCax)MnGaO5+δ, to display significant mixed conductivity and interesting magnetic properties by forming mixed manganese valence. Significant mixed valency in manganese has not previously been reported in Sr2MnGaO5, Ca2MnGaO5 or SrCaMnGaO5. Oxidation of Sr2MnGaO5, nominally Mn3+ to Sr2MnGaO5.5, nominally Mn4+, occurs rapidly without intermediates, whereas both Ca2MnGaO5 and SrCaMnGaO5 show no significant oxidation at atmospheric pressure. This work centres on the solid solution between these extremes to analyse structural changes and the potential for partial oxidation of manganese. Neutron diffraction has been carried out on these samples to investigate the structures and oxygen uptake