| La2Mo2O9 was reported as a new oxide-ion conductor recently. It has quite a fewoxygen vacancies in crystal lattice without doping low-valence metal cation, and theoxide-ion conductivity of La2Mo2O9 is higher than YSZ in middle temperature range of600～800℃.La2Mo2O9 was synthesized by sol-gel method. The ion conduction properties wereinvestigated by means of ac impedance spectroscopy, oxygen concentration cell etc. It wasshown a cubic-phased structure. The observed EMF values of oxygen concentration cellcoincided with theoretical values perfectly, indicating that it was purely oxide-ionicconductor with oxygen ion transference number of 1. It was shown to have the oxide ionicconductivity of 0.03 S·cm-1 at 1000℃.A series of La2(Mo1-xGax)2O9-α(x=0.05, 0.10, 0.15, 0.20) samples were preparedfor the first time by high-temperature solid-state reaction. X-ray powder diffraction patternshows that the samples are of single cubic phase of La2Mo2O9. Using the samples as solidelectrolytes and porous platinum as electrodes, the ion conduction properties of thesesamples were investigated by means of ac impedance spectroscopy, oxygen concentrationcell and oxygen pump (electrochemical oxygen permeation) at 600～1000℃in variousatmospheres. The observed EMF values of oxygen concentration cell coincided withtheoretical values perfectly, indicating that the ceramics were purely oxide-ionicconductors with oxygen ion transference number of 1 under oxygen atmosphere over thewhole temperature range. The electrochemical oxygen permeation rates determined were inaccordance with the theoretical rates calculated from Faraday's law, verifying directexperimentally that the oxide-ionic nature of the conduction under oxygen atmosphere. Athigh oxygen partialpressure range (pO2=10-5～105 Pa), they were almost pure ionicconductors, which was consistent with the result by means of oxygen concentration cell.Whereas at low oxygen partial pressure range (pO2=10-5～10-15Pa), the samplesexhibited mixed ionic and electronic conduction. The ionic conductivities of theseceramics are higher than 10-2 S·cm-1, which are obviously superior to the matrix La2Mo2O9, over the temperature range of 600～1000℃. La2Mo1.8Ga0.2O9 is shown to have the highestoxide ionic conductivity of 0.07 S·cm-1 at 1000℃. |
