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 <= 0.4, was prepared by a citrate-nitrate 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 570 degrees C 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 700 degrees C, 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 800 degrees C, which is nearly double that of the undoped material, and this is the highest value reported so far in this family of oxides. (c) 2005 The Electrochemical Society.