The electrical properties of La0.6Sr0.4Co1-yFeyO3 (LSCF, y=0-1.0) cathode materials were measured by DC four probes, X-ray photo-electron spectrum (XPS) was also introduced to determine the chemical state of Co, Fe ions in LSCF. It is found that the electrical conductivity of each sample has a maximum value with increasing temperature. XPS analysis shows that Co ion has three different chemical states, corresponding to two with Fe ion. The analyses indicates that the small-polaron hopping mechanism dominates the electron conduction at low temperature, while at high temperature, the three factors such as the thermally activated disproportionation of Co3+ ions into Co2+ and Co4+ pairs, the ionic compensation of oxygen vacancies formed at high temperatures, and Fe4+ ions charge compensation preferential to Co4+, all contribute to electrical conduction.
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