Preparation of LaNi1 − xFexO3 single phase and characterization of their phase transition behaviors

Optimization of preparation conditions of single phase LaNi1 − xFexO3, which is a candidate cathode material for solid oxide fuel cells (SOFC), by solid state reaction method was examined. We have found that heat treatment under O2 atmosphere is effective to prevent the generation of impurities with Ni valence less than 3+ and succeeded in the preparation of single phase specimens with x = 1.0 ~ 0.3. Using thermal analyses, Mössbauer spectroscopy and high temperature X-ray diffraction measurement, phase diagram of LaNi1 − xFexO3 has been constructed. Three kinds of phase transitions were observed in LaNi1 − xFexO3 and their phase boundary has been determined. Magnetic phase transition from antiferromagnetic to paramagnetic was observed for the specimens with x = 1.0 ~ 0.8. The magnetic phase transition temperature decreased with decreasing x and disappeared above room temperature in the specimens with x lower than 0.7. For LaFeO3, structural phase transition from orthorhombic distorted perovskite to trigonal distorted one was observed at 980 °C. By Ni substitution, high temperature trigonal phase varied to rhombohedral phase with decreasing structural phase transition temperature. neither phase transition nor oxygen nonstoichiometry was observed for the specimens with LaNi0.6Fe0.4O3 and LaNi0.7Fe0.3O3 from room temperature to 1000 °C, they can be regarded as promising candidate for cathode material of SOFC.