A comparative investigation of structural and optical properties of annealing modified mullite bismuth ferrite

Abstract Single phase Bi2Fe4O9 (Mullite BFO) nanoparticles were prepared first time by combustion method without using any solvent. Metal nitrates as oxidants and citric acid as fuel was used to synthesize Bi2Fe4O9 which were subsequently annealed at temperatures 550 °C, 600 °C and 650 °C. The impact of annealing temperature on crystal structure and physical properties are investigated by using X -ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Electron Dispersion Spectroscopy (EDS), Ultra Violet Visible (UV–vis) spectroscopic studies and Fourier Transformed Infrared Spectroscopy (FTIR). X-ray diffraction confirmed orthorhombic phase of the Mullite BFO and peak profile analysis has been carried out to study the crystallite development in Mullite BFO nanoparticles. The Mullite BFO annealed at 600 °C showed minimum lattice strain. Further, the FTIR and UV-Vis spectra of the samples at room temperature confirm the formation of orthorhombic structure of the samples. Our results revealed that the band gap of Mullite BFO nanoparticles reduces with increase in strain and lowest band gap attained for strained mullite BFO annealed at 650 °C is 2.0 eV. The correlation of annealing temperature with calculated lattice and structural parameter of Mullite BFO nanoparticles was established. Magnetic measurements were carried out at room temperature up to a field of 30 kOe. All samples of Mullite BFO showed weak ferromagnetic behavior. Magnetic hysteresis loops showed a significant increase in magnetization for sample annealed at 600 °C.