Properties of La 1− ySr yNi 1− xFe xO 3 as a cathode material for a low-temperature operating SOFC

Abstract

We synthesized Sr-doped La(Ni–Fe)O 3, or La 1− y Sr y Ni 1− x Fe x O 3 (LSNF), and investigated the composition and temperature dependence of the electronic properties and crystal structure of LSNF. The perovskite structure of LSNF is stable even at 1400 °C and in a single phase when its Fe concentration is higher than 0.5. The crystal structure and electronic conductivity of LSNF strongly depend on the composition. When the total concentration of Ni and Sr in this system is less than 0.4, it is in the orthorhombic phase. But the crystal structure symmetry improves (to the rhombohedral and then cubic phase) as the total concentration of Ni and Sr increases. The electronic conductivity values at 600 and 800 °C have sharp peaks when the composition is used as a parameter. The peak values are obtained when the total concentration of Ni and Sr is about 0.6 in this temperature range. The LSNF conductivity when the Ni and Sr concentration is high exhibits metallic temperature dependence. The conductivities drop sharply when the temperature exceeds about 600 °C. This implies that the oxygen vacancy concentration in the samples increases sharply at 600 °C or higher.