Synthesis and thermodynamic stability of multiferroic BiFeO3

Ceramic BiFeO3 samples were prepared by the sol gel combustion method using urea as fuel. The obtain powders were thermal treated at different temperatures (300-840 deg C) and times (1-64 h) to investigate the best synthesis conditions of the material. The resulting materials were analysed by TGA, FTIR, SEM/EDS and XRD. Rietveld analysis was applied to the diffraction data. The temperature and time of the heat treatment are critical for a high BiFeO3 phase content. Thermal treatment of 1 h at 600 deg C yielded 99% molar of the BiFeO3 phase with a mean particle size of 120 nm. Upper or lower calcinations temperatures yielded higher content of the secondary phases Bi2Fe4O9 and Bi25FeO39. Further heat treatment in air or in argon, up to 64 h, induces a decomposition of the BiFeO3 phase according to the reaction 49 BiFeO3 BiFeO3 - > 12 Bi2Fe4O9 + Bi25FeO39 pointing out that BiFeO3 is not thermodynamically stable at 600 deg C. The BiFeO3 decomposition follows Avrami-Erofeev law with a slope of 1 indicating a one-dimensional kinetics.