Dependence of thermal expansion of LaNi0.6Fe0.4O3 − δ and La0.6Sr0.4Co0.2Fe0.8O3 − δ on oxygen partial pressure

Abstract

The linear thermal expansion behavior of LaNi0.6Fe0.4O3−δ and La0.6Sr0.4Co0.2Fe0.8O3−δ, which have attracted much interest as cathode material for solid oxide fuel cell, was measured with dilatometer under various oxygen partial pressures, P(O2). Thermal expansion coefficient of LaNi0.6Fe0.4O3−δ is independent on P(O2) and between 1.20×10−5 K−1 and 1.35×10−5 K−1 in the measurement conditions of this study. Thermal expansion coefficient of La0.6Sr0.4Co0.2Fe0.8O3−δ is much larger than that of LaNi0.6Fe0.4O3−δ and increases with decreasing P(O2). The difference of P(O2) dependence of thermal expansion behavior between LaNi0.6Fe0.4O3−δ and La0.6Sr0.4Co0.2Fe0.8O3−δ could be ascribed to the difference of the dependence of oxygen nonstoichiometry on temperature and P(O2). Due to little variation of δ by temperature at constant P(O2) in LaNi0.6Fe0.4O3−δ, chemical expansion due to generation of δ scarcely contributes to total expansion, while chemical expansion largely contributes to total expansion of La0.6Sr0.4Co0.2Fe0.8O3−δ especially under low P(O2) owing to larger variation of δ by temperature at constant P(O2). By comparison with thermal expansion behavior of 8mol% yttria stabilized ZrO2, 8YSZ, under various P(O2), it was concluded that mechanical compatibility of LaNi0.6Fe0.4O3−δ against 8YSZ was better since La0.6Sr0.4Co0.2Fe0.8O3−δ showed not only much larger thermal expansion coefficient than 8YSZ but also large P(O2) dependence. Chemical expansion coefficients, ɛchem., of LNF64 and LSCF6428 were also evaluated. The ɛchem. of LNF64 was almost zero whereas those of LSCF6428 were order of 10−2, showing fair agreement with so far reported ɛchem. of LSCF and other oxide materials frequently used for SOFC.