Synthesis And Electrical Conductivity Of La_2-xSr_xM_o2O_9-α Ceramics

Oxide ion conductors have important and potential applications in solid oxide fuel cell, oxygen sensor and separation membrane etc. Recently, Lacorre and his coworker discovered that La₂Mo₂O₉ as a new type of oxide-ion conductor has higher oxide-ionic conductivity than that of conventional yttria stabilized zirconia(YSZ). However, up to now, most of the literatures on La₂Mo₂O₉ and doped La₂Mo₂O₉ reported mainly concerned with the characterization of structure and phase transformation, there has been no detailed work with respect to the conduction property on them.The aim of this thesis is to study the electrical properties of La₂Mo₂O₉-based oxides by various electrochemical methods.A series of La_2-xSr_xMo₂O₉(x=0, 0.05, 0.10, 0.15, 0.20) and La_1.95Sr_0.05Mo₂O₉ samples were prepared by high-temperature solid-state reaction and sol-gel method, respectively. The room temperature powder X-ray diffraction pattern of the ceramic samples show that they are of single cubic phase structure of La₂Mo₂O₉. Using the samples as solid electrolytes and porous platinum as electrodes, the ion conduction properties of these samples were investigated by means of impedance spectroscopy, oxygen concentration cell and oxygen pump(electrochemical oxygen permeation) at 550～1000℃in oxidizing and reducing atmospheres, respectively. The main results are as follows:(1) Under oxidizing atmospheres, La_2-xSr_xMo₂O₉ ceramic samples were all almost pure oxide ion conductors, the oxide ion conductivities were higher than 0.08S·cm^-1 at 1000℃, whereas under reducing atmosphere, the samples were mixed conductors of oxide-ion and electron.(2) The doping content x in the samples remarkably affected the electrical properties. La_1.9Sr_0.1Mo₂O₉ has the highest conductivity among the series of the La_2-xSr_xMo₂O₉ ceramics. Its oxide ion conductivity(0.15S·cm^-1 at 1000℃) was higher than that of YSZ.(3) The oxide-ion conductivity of La_1.95Sr_0.05Mo₂O₉ prepared by sol-gel method, whose sintered temperature was lower 50℃than solid-state reaction method, is higher than that of the sample prepared by solid-state reaction method under same determined conditions.