Preparation of LaNi 1 − xFe xO 3 single phase and characterization of their phase transition behaviors

Abstract

Optimization of preparation conditions of single phase LaNi 1 − x Fe x O 3, 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 O 2 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 LaNi 1 − x Fe x O 3 has been constructed. Three kinds of phase transitions were observed in LaNi 1 − x Fe x O 3 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 LaFeO 3, 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. Since neither phase transition nor oxygen nonstoichiometry was observed for the specimens with LaNi 0.6Fe 0.4O 3 and LaNi 0.7Fe 0.3O 3 from room temperature to 1000 °C, they can be regarded as promising candidate for cathode material of SOFC.