Abstract
This paper describes the results of electron microscopy, high-temperature powder neutron diffraction, and impedance spectroscopy studies of brownmillerite-structured Ba2In2O5 and perovskite structured Ba(InxZr1−x)O3−x/2. The ambient temperature structure of Ba2In2O5 is found to adopt Icmm symmetry, with disorder of the tetrahedrally coordinated (In3+) ions of the type observed previously in Sr2Fe2O5. Ba2In2O5 undergoes a ∼6-fold increase in its ionic conductivity over the narrow temperature range from ∼1140 K to ∼1230 K, in broad agreement with previous studies. This transition corresponds to a change from the brownmillerite structure to a cubic perovskite arrangement with disordered anions. Electron microscopy investigations showed the presence of extended defects in all the crystals analyzed. Ba(InxZr1−x)O3−x/2 samples with x=0.1 to 0.9 adopt the cubic perovskite structure, with the lattice parameter increasing with x.
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