Thermodynamic stability of LaNi1-xFexO3-δ (x = 0.0, 0.2, 0.4), which is expected as new cathode material for solid oxide fuel cells, was investigated by thermogravimetry and high-temperature X-ray diffraction under controlled oxygen partial pressure, P(O2). It was clarified that LaNiO3-δ decomposed through La4Ni3O10 to La2NiO4 with increasing temperature under P(O2) of 10-2 atm or more. The decomposition temperature decreased with reducing P(O2). Under P(O2) of 10-3 atm, LaNiO3-δ directly decomposed to La2NiO4. The decomposition of LaNi1-xFexO3-δ (x = 0.2, 0.4) to La4(Ni1-xFex)3O10 was also observed, and Ellingham diagram of the decomposition reaction was prepared. It was revealed that thermodynamically stable temperature and P(O2) region expanded with increasing Fe content. Nonlinear decomposition boundary was observed in the Ellingham diagram of LaNiO3-δ and LaNi0.8Fe0.2O3-δ whose origin can be suspected to the difference of δ at the decomposition on P(O2). Linear decomposition boundary was observed for LaNi0.6Fe0.4O3-δ, indicating variation of entropy, ΔS°, and enthalpy, ΔH°, at the decomposition were 151 J mol-1 K-1 and 240 kJ mol-1, respectively.
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Physical and Theoretical Chemistry