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

Highlights: • Tailored optical bandgap from 2.08 ± 0.02 eV to 1.59 ± 0.02eV via competing impact of Co substitution and thermal treatment temperature. • Detailed investigation on structural, morphological and optical properties of Co doped BFO. • Detailed investigation on impact of annealing temperature on the physical properties of Co doped BFO. 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 BiFe_0.9Co_0.1O₃ 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 BiFe_0.9Co_0.1O₃ 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 BiFe_0.9Co_0.1O₃ 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.