Synthesis and characterization of La0.6Sr0.4−xCaxCo0.2Fe0.8O3 materials by the gel-casting process

Abstract

La0.6Sr0.4−xCaxCo0.2Fe0.8O3 (LSCCF) powders were prepared from relative oxides and carbonate powders by a gel-casting process. Phase structure of the obtained powders with different calcium dosages (x=0.0, 0.2, 0.4) was investigated. Density and porosity of the sintered LSCCF samples were measured by the Archimedes method. Microstructure was observed by scanning electron microscope (SEM) and electrical conductivity of the specimens was tested using the four-probe method. Effects of calcium dosage on the thermal expansion coefficient (TEC) of the sintered LSCCF samples were also studied. The results showed that superfine and well-dispersed LSCCF powders with perovskite structure were obtained when the dried gels were calcined at temperature above 1000°C. The calcium dosage and sintering temperature have an obvious influence on the density and pore characteristics of the LSCCF samples. Open porosities of LSCCF samples sintered at different temperature vary from 4.7% to 50.2%, decreasing as calcium dosage and sintering temperature increase. Thermal expansion coefficients of the LSCCF materials also greatly depend on calcium dosage. A typical TEC value of 13.05×10−6K−1 for La0.6Sr0.2Ca0.2Co0.2Fe0.8O3 samples was obtained at 800°C, lower than values obtained for samples with no calcium dosage. Electrical conductivity of the LSCCF samples decreases as calcium dosage increases, but all samples showed a conductivity value above 300Scm−1 at 400–800°C, which can satisfy the requirements of cathode materials for solid oxide fuel cells.