The precursors of La0.9M0.1Ga0.8Mg0.2O3–α (M＝Ca2＋, Sr2＋, Ba2＋) were prepared by a hydrothermal precipitation method in which the precipitant was from hydrolysis of urea (CO(NH2)2) in water solution under hydrothermal conditions. The ceramic samples were obtained by calcining and sintering the precursors. XRD showed the ceramic samples to be of a single orthorhombic phase of LaGaO3 perovskite structure. The proton conduction in La0.9M0.1Ga0.8Mg0.2O3－α was confirmed by an isotope effect and a hydrogen pumping experiment. Protonic conductivity was measured by an AC impedance spectroscopy method from 300 to 600 ℃ in a hydrogen atmosphere, which depended on the alkaline earth cations doped for the La site and increased in the following order: σ(M＝Sr2＋)＞σ(M＝Ba2＋)＞σ(M＝Ca2＋). Ammonia synthesis at atmospheric pressure was carried out using La0.9M0.1Ga0.8Mg0.2O3–α as electrolyte, and it was found that the optimum temperature for ammonia synthesis in this study was 520 ℃. The rate of NH3 formation was 1.63×10–9 mol•s－1•cm－2 (M＝Ca2＋), 2.53×10–9 mol•s－1•cm－2 (M＝Sr2＋) and 2.04×10–9 mol•s－1•cm－2 (M＝Ba2＋) at 520 ℃ when a current density of 1 mA•cm–2 was imposed on the cell, respectively.

Key words: LaGaO3, hydrothermal precipitation, proton conduction, ammonia synthesis