Application of La0.6AE0.4MnO3 (AE=Ca and Sr) to electric current collectors in high-temperature solid oxide fuel cells

The crystallographic, mechanical, thermal and electrical properties of La0.6AE0.4MnO3 perovskites (AE=Ca and Sr) have been investigated. La0.6Ca0.4MnO3 showed an orthorhombic symmetry at room temperature, and its symmetry changed into tetragonal at approximately 500 °C and into cubic at approximately 900 °C. La0.6Sr0.4MnO3 showed tetragonal symmetry at room temperature and its symmetry changed into cubic at temperatures ≥90 °C. Transgranular fracture of dense La0.6AE0.4MnO3 specimens, after mechanical strength measurements at temperatures ≤400 °C, was indicated, whereas the specimens mechanically tested after the measurement at temperatures ≥600 °C showed intergranular fracture. Thermal expansion coefficients (TECs) of the sintered specimens in the temperature range from 50 to 1000 °C were 11.7×10−6/°C for La0.6Ca0.4MnO3 and 12.2×10−6/°C for La0.6Sr0.4MnO3. Electrical conductivities of the dense specimens at 1000 °C were 227 S/cm for La0.6Ca0.4MnO3 and 213 S/cm for La0.6Sr0.4MnO3. To synthesize these materials as electric current collectors in high-temperature solid oxide fuel cells (SOFC), La0.6AE0.4MnO3 perovskites were compounded with manganese oxide. The TECs of the composites at around 50 vol.% Mn3O4 were almost the same as that of the Y2O3 stabilized ZrO2 (YSZ) electrolyte. Electrical conductivities of these dense specimens at 1000 °C were observed to be between 50 and 90 S/cm. Thus, dense La0.6AE0.4MnO3–Mn3O4 composites are appropriate for the electric current collectors in the SOFC.