Sintering and electrical conductivity in fast oxide ion conductors La2−xRxMo2−yWyO9 (R: Nd, Gd, Y)

Attrition and ball milling are used as mechanical means to reduce grain size of optimized fast oxide-ion conductors La2−xRxMo2−yWyO9 (R: rare earths). Dilatometry is used to determine the optimal sintering conditions in order to obtain high density samples (greater than 96% of relative density) with help of scanning electron microscopy to characterize their microstructure. The optimal sintering temperatures are highly dependent on the chemical composition, and therefore identical annealing temperatures do not warrant similar relative densities. Complex impedance spectroscopy show that above the transition temperature of La2Mo2O9 at 580 °C, the conductivity of all the studied compounds is lower than that of the parent compound, whereas just below the transition, in most cases the stabilization of the cubic phase increases conductivity. An interesting result is that tungsten substitution, which stabilizes La2Mo2O9 against reduction, does not affect significantly the oxide ion conduction.