Synthesis and characterization of calcium and manganese-doped rare earth oxide La1-xCaxFe0.9Mn0.1O3-δ for cathode material in IT-SOFC

In order to develop novel cathode materials with high performance for intermediate temperature SOFC (IT-SOFC), Ca and Mn doped rare earth oxides La1-xCaxFe0.9Mn0.1O3-δ (x=0.1, 0.3 and 0.5, denoted as LCFM9191,LCFM7391 and LCFM5591) were synthesized by solid state reaction (SSR) method. The formation process, phase structure and microstructure of the synthesized samples were characterized using thermogravimetry/differential scanning calorimetry (TG/DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The thermal expansion coefficients (TEC) of the samples were analyzed at 100–900 °C by thermal dilatometry. The electrical conductivities of the samples were measured with direct current (DC) four-terminal method from 300 to 850 °C. The results indicated that the samples (x=0.1 and 0.3) exhibited a single phase with orthorhombic and cubic perovskite structure, respectively after being sintered at 1200 °C for 3 h. The electrical conductivity of the samples increased with temperature up to a maximum value, and then decreased. The small polaron hopping was regarded as the conducting mechanism for synthesized samples at T≤600 °C. The negative temperature dependence occurring at higher temperature was due to the creation of oxygen vacancies for charge balance. LCFM7391 had higher mixed conductivity (>100 S/cm) at intermediate temperature and could meet the demand of cathode material for IT-SOFC. In addition, the average TECs of LCFM9191 and LCFM7391 were 11.9×10−6 and 13.1×10−6 K−1, respectively, which had good thermal match to the common electrolytes.