La_(0.6)Sr_(0.4)Co_(1-y)Fe_yO_3(y=0-1.0) powders were synthesized by a citrate method,and the structure and mixed electronic-ionic conducting properties of the resulting ceramics were investigated. The synthesized La_(0.6)Sr_(0.4)Co_(1-y)Fe_yO_3 powders have a pure perovskite structure and consist of uniform and fine particles.A perovskite structure with rhombohedral symmetry was certified for the La_(0.6)Sr_(0.4)Co_(1-y)Fe_yO_3 ceramics.The increase of Co/Fe ratio significantly promoted the grain growth and microstructural densification. The La_(0.6)Sr_(0.4)Co_(1-y)Fe_yO_3 compositions with relatively higher Co/Fe ratio exhibit superior mixed conducting properties.The electronic structure and microstructure of the ceramics are responsible for the variation of the mixed conducting properties with Co/Fe ratio.
Ln 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3 (Ln=La,Pr,Nd,Sm)perovskite-type complex oxides were synthesized using a glycine-nitrate process,and the structure,electrical conducting and thermal expansion properties of the resulting ceramics were examined with regard to the nature of the lanthanide cations.The results indicated that the La,Pr and Nd specimens had a rhombohedral symmetry,while an orthorhombic structure was determined for the Sm specimen.The pseudo-cubic lattice constant decreased with smaller lanthanide cations.It was found that the electrical conducting properties declined with decreasing lanthanide cation size.Fortunately, all the compositions remained rather high electrical conductivities exceeding 650Ω-1·cm-1 in the intermediate temperature range(600-800℃).An appreciable thermal expansion increase at high temperatures was detected for all the compositions.Decreasing the size of the lanthanide cations resulted in an increase of thermal expansion.With respect to the high electrical conductivities,the Ln 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3 oxides are considered to be acceptable as mixed conducting component in composite cathode designs together with doped ceria electrolytes.
