Synthesis and characterization of La2MO2O9 obtained from freeze-dried precursors

La2Mo2O9 ceramics have been prepared from freeze-dried precursors and their properties compared to those of lantanum molybdate obtained by conventional solid state (SS) reaction. All materials have been characterized by X-ray diffraction, scanning electron microscopy and thermal analysis (TGA/DTA/DSC and dilatometry) to characterize the phase formation and phase transition. When the freeze-dried method was applied, the synthesis temperature required to obtain dense samples was much lower than that for powders obtained by SS reaction. The morphology and structure of the oxide particle are significantly dependent on the synthesis method. The grain size is smaller, whereas the density of sintered pellets is higher for the freeze-dried precursor powder when compared with the SS reaction method. Impedance spectroscopy was used to measure the electrical conductivity of La2Mo2O9 from 548 to 1123 K, in air, and to characterize the blocking effects of grain boundaries. (C) 2004 Elsevier Inc. All rights reserved.