Key Laboratory of Organic Synthesis of Jiangsu Province, School of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou, Jiangsu 215123, China

A series of La0.90Ba0.10Ga1－xMgxO3－a (x＝0.20, 0.25 and 0.30) ceramics with a perovskite-type orthorhombic structure were prepared by the conventional solid-state reaction. Their conduction was studied in wet hydrogen, wet air and dry air atmospheres by various electrochemical methods including AC impedance spectroscopy, isotope effect, electrochemical hydrogen pumping, steam concentration cells and oxygen concentration cells from 873 to1273 K. Proton conduction was confirmed directly by an electrochemical hydrogen-pumping experiment. The hydrogen evolution rates coincided with theoretical ones calculated from Faraday’s law, indicating that in hydrogen atmosphere the charge carriers were predominantly protons. Isotope effect confirmed the ceramic samples possessed proton conduction under water vapor-containing atmosphere. In wet air atmosphere, the samples were found to be mixed (proton＋oxide ion＋hole) conductors, and in dry air atmosphere to be mixed (oxide ion＋hole) conductors. These results were different from the reports that BaO- and MgO-doped LaGaO3 ceramics were mixed conductors of oxide ion and electron hole in O2 and air; whereas they were oxide ion conductors in N2 and H2 atmospheres.