Significant effects of sintering temperature on the performance of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ oxygen selective membranes

In this work, the effects of sintering temperature on the phase structure, oxygen nonstoichiometry, microstructure, electrical conductivity, and oxygen permeation behavior of perovskite La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ membranes were systematically studied. The sintering temperature has negligible effect on the bulk properties of the phase structure and the oxygen nonstoichiometry, but has significant influence on the microstructure and electrical conductivity of the membranes, and therefore imposes large impact on its oxygen permeability. With an increase in the sintering temperature, the grain size increased steadily from 0.3 μm at 1000 °C to 3.5 μm at 1300 °C, accompanied with the substantial enhancement of electrical conductivity but the decrease of activation energy for the electrical conduction. Results indicate that the grain boundary had a much lower electrical conductivity than that of the bulk. The oxygen permeation process was mainly rate-determined by the slow oxygen diffusion over the grain boundary. Higher sintering temperature lowers the activation energy for oxygen permeation and accordingly gives rise to higher oxygen permeation flux. The oxygen permeation flux could be improved more than 10 times if the sintering temperature increased from 1000 to 1300 °C.