Nb-Doped La2Mo2O9: A New Material with High Ionic Conductivity

A new series of La2Mo2O9-based oxides of the general formula La2Mo2-xNbxO9-delta, where x < or = 0.4, was prepared by a citratenitrate combustion process, and the electrical and thermal properties were evaluated. Electrical conductivity measurements on the sintered samples confirmed that all the compositions underwent a phase transition below 570DGC with a concomitant increase in the oxide-ion conductivity. Although Nb doping did not suppress the order-disorder transition exhibited by pure La2Mo2O9 completely, it has significantly lowered both the transition temperature and the enthalpy change associated with the transition. The oxide-ion conductivity was found to decrease with increasing Nb concentration, and at 700DGC, La2Mo2-xNbxO9-delta compositions with x values of 0.06 and 0.1 exhibited oxide-ion conductivities of 0.069 and 0.062 S/cm, respectively. The composition with the lowest Nb doping, viz., La2Mo1.94Nb0.06O9-delta. exhibited an oxide-ion conductivity of 0.113 S/cm at 800DGC, which is nearly double that of the undoped material, and this is the highest value reported so far in this family of oxides.