The effects on the structures and properties in the oxide-ion conductor La 2Mo 2O 9 by partial substituting Ba for La

Abstract

The oxide-ion conductors (La 1− x Ba x ) 2Mo 2O 9− δ ( x = 0.02–0.10) were prepared by a solid-state reaction method. The formation process of the La 2Mo 2O 9 phase in the samples was investigated using a thermal dilatometer. The effects on the structures and properties in the oxide-ion conductor La 2Mo 2O 9 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 La 2Mo 2O 9, and the solubility of Ba in (La 1− x Ba x ) 2Mo 2O 9− δ , was determined. The results show that the formation process of the La 2Mo 2O 9 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 (La 1− x Ba x ) 2Mo 2O 9− δ is around x = 0.08. When x > 0.02, the structural phase transition in La 2Mo 2O 9 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 (La 1− x Ba x ) 2Mo 2O 9− δ reaches a maximum of 0.046 and 0.075 S/cm at 800 and 850 °C, respectively.