Tunable bandgap in cobalt doped bismuth ferrite nanoceramics: The role of annealing temperature

Abstract

Recent years have witnessed an exotic interest in the bandgap tailoring of multiferroic materials for photovoltaic and photocatalytic applications owing to their fascinating physical properties. To enhance the absorption of the solar spectrum, an attempt is made to tune the optical bandgap and investigate the influence on structural, morphological, and optical properties of BiFe0.9Co0.1O3 nanocrystals by controlling thermal annealing temperature. Herein, nanoparticles of undoped and cobalt (10 mol %) doped BiFeO3 are synthesised using citrate precursor technique and annealed at different temperatures (500 °C, 550 °C, and 600 °C). X-ray diffraction studies confirm the rhombohedrally distorted perovskite structure for all the samples. An increasing trend of particle size with the increase in thermal annealing temperature was observed. Microstructural analysis revealed spherical shaped grains for BiFe0.9Co0.1O3 samples. X-ray photoelectron spectroscopy studies confirmed the chemical states of all the constituent elements and validated the presence of oxygen vacancies in our samples. The optical absorption coefficient was found to increase by 45% in BiFe0.9Co0.1O3 compared to pure BiFeO3 at 400 nm. The optical bandgap value of bismuth ferrite was reduced from (2.08 ± 0.02) eV to (1.59 ± 0.02) eV with a combined impact of cobalt doping and thermal annealing temperature. Also, an inverse correlation of bandgap values and thermal annealing temperature was observed. Therefore, this study suggests that control on thermal annealing temperature has a decisive effect on the optical bandgap of complex oxide nanocrystals.