p(O2)-stability of LaFe1-xNixO3-δ solid solutions at 1100 oC

LaFe1-xNixO3-δ (x=0.1-1.0) perovskites were synthesized via citrate route. The p(O2)-stability of the perovskite phases LaFe1-xNixO3-δ has been evaluated at 1100 oC based on the results of XRD analysis of powder samples annealed at various p(O2) and quenched to room temperature. The isothermal LaFeO3-δ-'LaNiO3-δ' cross-section of the phase diagram of the La-Fe-Ni-O system has been proposed in the range of oxygen partial pressure -15<log p(O2)/atm≤0.68. The unit cell parameters of orthorhombic perovskites O-LaFe1-xNixO3-δ increase with decrease in p(O2) at fixed composition x. This behavior is explained on the basis of size factor. The decomposition temperatures of rhombohedral phases R-LaFe1-xNixO3-δ for x=0.7, 0.8, 0.9 and 1.0 in air were determined as 1137, 1086, 1060 and 995 oC, respectively. - Graphical abstract: Isothermal LaFeO3-δ-'LaNiO3-δ' section of the phase diagram of the La-Fe-Ni-O system at 1100 oC. The hatched areas represent single phase regions: O-LaFe1-xNixO3-δ (x≤0.4) with orthorhombically distorted perovskite structure and R-LaFe1-xNixO3-δ (0.6≤x<0.8) with rhombohedral one.