Characterization of perovskite systems derived from Ba2In2O5□: Part I: the oxygen-deficient Ba2In2(1−x)Ti2xO5+x□1−x (0≤x≤1) compounds

Ba2In2(1−x)Ti2xO5+x□1−x (0≤x≤1) compounds have been prepared by solid state reaction. At room temperature (RT), when x increases, the progressive filling of oxygen vacancies, concomitant with the substitution of Ti for In, first induces (for 0<x≤0.075) a disorder in the plane of oxygen vacancies observed in Ba2In2O5□. Then, it suppresses the distortion to orthorhombic symmetry; for 0.075<x≤ 0.15, the symmetry becomes tetragonal and a formation of domains is observed. For 0.15<x<1, all members adopt a disordered cubic perovskite (DCP) structure at RT. tivity measurements between 450 and 800 °C show that the change from brownmillerite to tetragonal structure when x increases from 0.075 to 0.1 induces a drastic decrease of the activation energy. The highest oxide-ion conductivity is observed for 0.1≤x≤0.33: ∼0.5×10−2 S cm−1 at 700 °C.