Preparation of nanocrystalline BiFeO3 and kinetics of thermal process of precursor

The Bi₂Fe₂(C₂O₄)₅·5H₂O was synthesized by solid-state reaction at low heat using Bi(NO₃)₃·5H₂O, FeSO₄·7H₂O, and Na₂C₂O₄ as raw materials. The nanocrystalline BiFeO₃ was obtained by calcining Bi₂Fe₂(C₂O₄)₅·5H₂O at 600 °C in air. The precursor and its calcined products were characterized by thermogravimetry and differential scanning calorimetry, FT-IR, X-ray powder diffraction, and vibrating sample magnetometer. The data showed that highly crystallized BiFeO₃ with hexagonal structure space group R3c(161)] was obtained when the precursor was calcined at 600 °C in air for 1.5 h. The thermal process of the precursor in air experienced five steps which involved, at first, the dehydration of an adsorption water molecule, then dehydration of four crystal water molecules, decomposition of FeC₂O₄ into Fe₂O₃, decomposition of Bi₂(C₂O₄)₃ into Bi₂O₃, and at last, reaction of Bi₂O₃ and Fe₂O₃ into hexagonal BiFeO₃. Based on Starink equation, the values of the activation energies associated with the thermal process of Bi₂Fe₂(C₂O₄)₅·5H₂O were determined. Besides, the most probable mechanism functions and thermodynamic functions (ΔS ^≠, ΔH ^≠, and ΔG ^≠) of thermal processes of Bi₂Fe₂(C₂O₄)₅·5H₂O were also determined.