Effect of calcination temperature on structural and morphological properties of bismuth ferrite nanoparticles

Bismuth Ferrite (BiFeO3) is one such materials which has shown very promising multiferroic and excellent optical properties. In this paper, we report effect of annealing temperature on the structural, morphological and optical properties of BiFeO₃ nanoparticles synthesised through sol-gel auto-combustion method. Nanoparticles prepared were calcined at three different temperatures, 400 °C, 500 °C and 600 °C, and named as BFO1, BFO2 and BFO3, respectively. X-ray diffraction confirmed the rhombohedral structure with R3c space group as a primary phase. However, a secondary phase Bi₂Fe₄O₉ was also observed which decreases with increasing temperature. The crystallite sizes were found to increase with increasing temperature with BFO2 as anomaly. Field emission scanning electron microscopy (FESEM) shows clear grain formation for all the samples. TEM micrographs and SAED patterns show crystalline grains with rhombohedral structure. All the functional groups observed in the Fourier infrared spectroscopy (FTIR) measurement are indexed. The FTIR spectra shows presence of two prominent vibrational modes in the wave number range 447 and 560 cm^-1 corresponding to the stretching of Fe-O bonds. Raman analysis shows presence of a peak at ~527 cm^-1 for (BFO3) which was absent in other two samples. Also, the intensity of the A₁-1 mode was found stronger than that of A₁-2 mode in all the samples which confirmed the stability of the structure, except for BFO1.