The crystal structures, microstructure and ionic conductivity of Ba2In2O5 and Ba(InxZr1-x)O3-x/2

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 Ba(2)In(2)O(5)is found to adopt Icmm symmetry, with disorder of the tetrahedrally coordinated (In3+) ions of the type observed previously in Sr2Fe2O5. Ba2In2O5 undergoes a similar to 6-fold increase in its ionic conductivity over the narrow temperature range from similar to 1140 K to similar 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 show 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. (C) 2002 Elsevier Science (USA).