Study on the electrical conductivity and oxygen diffusion of oxide-ion conductors La2Mo2−xTxO9−δ (T = Al, Fe, Mn, Nb, V)

In this paper, the influence of cationic substitutions at Mo site with Al³⁺, Fe³⁺, Mn⁴⁺, Nb⁵⁺ and V⁵⁺ ions on the structure, oxygen ion diffusion and electrical properties in La₂Mo₂O₉ oxide-ion conductors have been investigated by X-ray diffraction method, dielectric relaxation technique and direct current conductivity measurement. Except for V⁵⁺ substitution all of these substitutions up to 5% cannot suppress the phase transition in La₂Mo₂O₉. In the dielectric measurement, one prominent relaxation peak is observed in temperature spectrum as well as in frequency spectrum, which is associated with the short-distance diffusion of oxygen vacancies. The activation energy for oxygen ion diffusion is deduced as in the range of 1-1.1 eV for Al, Fe, Mn and Nb doped samples and 1.4-1.5 eV for V doped samples. All substituted samples have a higher conductivity than the un-doped compound. In the Al, Fe, Mn and Nb substituted materials the phase transition is not suppressed; however, K substitution at the La site can completely suppress the transition and maintains high conductivity at low temperature.