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

Abstract

The crystallographic, mechanical, thermal and electrical properties of La(0.6)AE(0.4)MnO(3) 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 degreesC and into cubic at approximately 900 degreesC. La0.6Sr0.4MnO3 showed tetragonal symmetry at room temperature and its symmetry changed into cubic at temperatures greater than or equal to90 degreesC. Transgranular fracture of dense La(0.6)AE(0.4)MnO(3) specimens, after mechanical strength measurements at temperatures less than or equal to400 degreesC, was indicated, whereas the specimens mechanically tested after the measurement at temperatures greater than or equal to600 degreesC showed intergranular fracture. Thermal expansion coefficients (TECs) of the sintered specimens in the temperature range from 50 to 1000degreesC were 11.7 x 10(-6)/,C for La0.6Ca0.4MnO3 and 12.2 x 10(-6)/degreesC for La0.6Sr0.4WO3. Electrical conductivities of the dense specimens at 1000 degreesC 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), La(0.6)AE(0.4)MnO(3) 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 degreesC were observed to be between 50 and 90 S/cm. Thus, dense La(0.6)AE(0.4)MnO(3)-Mn3O4 composites are appropriate for the electric current collectors in the SOFC. (C) 2003 Elsevier B.V. All rights reserved.