Raman study of BiFeO3 nanostructures using different excitation wavelengths: Effects of crystallite size on vibrational modes

Bismuth ferrite (BiFeO3) is a perovskite metal oxide well known because of its multifunctional properties. In this study, we report Raman analysis of BiFeO3 nanostructures synthesized using the sol-gel method at different annealing conditions. The synthesis was conducted at two different annealing temperatures of 500 degrees C and 600 degrees C, and three different annealing rates of 2, 5, and 10 degrees C/min. The crystallite sizes and particle sizes were evaluated for the obtained nanostructures using X-ray diffraction and scanning electron microscopy. Raman scattering study was conducted for the prepared BiFeO3 samples at different excitation wavelengths in the visible and near-infrared region (457 nm, 532 nm, 633 nm, and 785 nm). The variations in the features of the Raman modes with different excitation wavelengths and annealing conditions were examined in detail. Resonant Raman scattering was observed when the excitation energy was comparable to or greater than the bandgaps of the BiFeO3 nanostructures, where the intensities of the A(1)-3, E-3, and E-4 vibrational modes increased. The variations in the relative intensities and areas of the A(1)-2 and A(1)-1 modes with the crystallite size were correlated with the occurrence of size-dependent magnetic properties in BiFeO3.