Synthesis, sinterability and ionic conductivity of nanocrystalline La2Mo2O9 powders

A modified freeze-dried method has been used to obtain polycrystalline powders of the ionic conductor La2Mo2O9. Such ceramic powders were characterized by TG/DTA, XRD, SEM and TEM, and their sinterability was analysed by dilatometry and isothermal sintering studies. The nanocrystalline powders possessed high reactivity and good sinterability, producing dense pellets at only 1023 K with an average grain size of 1.5 μm. Bulk and grain boundary conductivities of La2Mo2O9 have been investigated by impedance spectroscopy in samples sintered in a range of temperatures, i.e. between 1023 and 1373 K, and their magnitudes correlated with the microstructure. A significant grain boundary resistance was found for sintered samples prepared at temperatures below 1173 K, causing a pronounced decrease in the overall conductivity, even at high temperature. This contribution however was minimised upon sintering at temperatures above 1173 K, yielding ionic conductivity values of 0.12 S/cm at 1073 K.