Analysis of thermal stability of LaNi1-xFexO3-δ (x=0.0, 0.2, 0.4) by thermogravimetry and high-temperature X-ray diffraction under controlled oxygen partial pressures

Thermodynamic stability of LaNi1-xFexO3-delta (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(O-2). It was clarified that LaNiO3-delta decomposed through La4Ni3O10 to La2NiO4 with increasing temperature under P(O-2) of 10(-2) atm or more. The decomposition temperature decreased with reducing P(O-2). Under P(O-2) of 10(-3) atm, LaNiO3-delta directly decomposed to La2NiO4. The decomposition of LaNi1-xFexO3-delta (x = 0.2, 0.4) to La-4(Ni1-xFex)(3)O-10 was also observed, and Ellingham diagram of the decomposition reaction was prepared. It was revealed that thermodynamically stable temperature and P(O-2) region expanded with increasing Fe content. Nonlinear decomposition boundary was observed in the Ellingham diagram of LaNiO3-delta and LaNi0.8Fe0.2O3-delta whose origin can be suspected to the difference of delta at the decomposition on P(O-2). Linear decomposition boundary was observed for LaNi0.6Fe0.4O3-delta , indicating variation of entropy, Delta SA degrees, and enthalpy, Delta HA degrees, at the decomposition were 151 J mol(-1) K-1 and 240 kJ mol(-1), respectively.