Dielectric relaxation studies on the submicron crystalline La2Mo2O9 oxide-ion conductors

Submicron crystalline La2Mo2O9 bulk samples with grain size of about 0.3 μm were successfully synthesized by sol–gel method and sintering process assisted by phase transformation. In the dielectric measurement, two prominent relaxation peaks with almost the same height (Pd1 at lower-temperature and Pd2 at higher-temperature) are observed in temperature spectrum as well as in frequency spectrum, which are associated with the short-distance diffusion of oxygen vacancies. The activation energies and relaxation times at infinite temperature of these two peaks are deduced as (1.22 eV, 3.3×10−16 s) and (1.35 eV, 5.9×10−16 s), respectively. The DC conductivity of the submicron crystalline samples, which is about 0.02 S/cm when extrapolated to 800 °C, is much smaller than that of the macrocrystalline samples. The reciprocal of the peak height for Pd1 peak is linearly proportional to temperature, while that for Pd2 peak is temperature independent. The reason for the co-appearance and the possible relaxation dynamics of the two peaks are discussed.