Crystal structure of brownmillerite Ba2InGaO5

Ba2InGaO5 was prepared by high-temperature solid-state reaction. This compound adopts a brownmillerite structure below 1200 °C, which was not found in past studies of Ba2(In1−xGax)2O5. Combined structure refinements against neutron and X-ray powder diffraction data show that this material adopts a layered ordering of In and Ga. This is one of a few examples of such an ordering in the brownmillerite structure solely due to size difference between the B cations. This ordering further stabilizes the brownmillerite crystal structure compared to other compositions at smaller Ga contents (x<0.5), for which the transition to a disordered cubic perovskite occurs at a much lower temperature. As could be expected, such stronger ordering is detrimental to ionic conductivity.