The effects on the structures and properties in the oxide-ion conductor La2Mo2O9 by partial substituting Ba for La

The oxide-ion conductors (La1−xBax)2Mo2O9−δ (x = 0.02-0.10) were prepared by a solid-state reaction method. The formation process of the La2Mo2O9 phase in the samples was investigated using a thermal dilatometer. The effects on the structures and properties in the oxide-ion conductor La2Mo2O9 by partially substituting Ba for La were studied using X-ray diffraction, ac impedance spectroscopy and thermal dilatometry, respectively. The minimum doping content of Ba, which can suppress the structural phase transition in La2Mo2O9, and the solubility of Ba in (La1−xBax)2Mo2O9−δ, was determined. The results show that the formation process of the La2Mo2O9 phase presents an expansion process due to the introduction of oxygen vacancies. With the increase of the Ba doping contents, the lattice constant decreases at first and then increases. The lattice constant attains a peak at x = 0.08, and therefore, it is concluded that the solid solution limit of Ba in (La1−xBax)2Mo2O9−δ is around x = 0.08. When x > 0.02, the structural phase transition in La2Mo2O9 can be completely suppressed through the partial substitution of Ba for La as demonstrated by the observation of both electrical and thermal properties. For x = 0.08, the conductivity of the oxide-ion conductor (La1−xBax)2Mo2O9−δ reaches a maximum of 0.046 and 0.075 S/cm at 800 and 850 °C, respectively.