Preparation of nanocrystalline BiFeO3 and kinetics of thermal process of precursor

Abstract

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.