Optimizing phase formation of BiFeO3 and Mn-doped BiFeO3 nanoceramics via thermal treatment using citrate precursor method

Abstract

In recent years, bandgap tailoring of ferroelectric materials has gained great attention in the scientific community owing to their favourable materials characteristics, and new endowing paths for developing multifunctional devices. In this study, an attempt was made to tune the optical bandgap of BiFeO3 (BFO) via chemical substitution and by controlling thermal treatment temperature and time. A series of BiFe1-xMnxO3 (x = 0.00, 0.03, 0.05) nanoceramic samples were prepared by adopting the citrate precursor method. The effect of Mn substitution, annealing temperature, and annealing time on structural, morphological, and optical properties of BFO was investigated using X-ray diffraction, field emission scanning electron microscopy, and UV–visible spectroscopy, respectively. The average crystallite size was found to decrease (from 44−17 nm) with Mn-doping and increase with increasing annealing temperature and time (from 17−27 nm) due to the agglomeration of nanoparticles. The FESEM studies revealed the inhomogeneous distribution of granular structured grains with negligible porosity. The optical bandgap energy of BFO nanoparticles was found to reduce significantly by 21% (2.08−1.62 eV) with a competing effect of Mn-substitution, annealing temperature, and annealing time. The optical bandgap studies of BiFe0.97Mn0.03O3 showed a direct correlation with annealing temperature and an inverse correlation with annealing time. Additionally, BiFe0.97Mn0.03O3 nanoparticles annealed at 550 °C for 2 h showed a 31% enhancement in absorption coefficient and 14% reduction in bandgap value without a structural phase transition. The results obtained in this study propose BiFe0.97Mn0.03O3 nanoparticles as a potential candidate for upcoming ferroelectric photovoltaic devices.