Structural, morphological, optical and dielectric investigations in cobalt doped bismuth ferrite nanoceramics prepared using the sol-gel citrate precursor method

Abstract In this work, the synthesis of un-doped and cobalt (Co)-doped nanoceramic samples of bismuth ferrite by cost-effective sol-gel citrate precursor technique are presented. Detailed investigations have been attempted to study the effect of Co substitution on the structural, morphological, dielectric and optical properties of bismuth ferrite prepared using the citrate precursor method. The main feature of these investigations is the relative elimination of secondary phase formation while preparing bismuth ferrite nanoceramic samples. X-ray diffraction analysis shows distorted rhombohedral perovskite structure for all compositions of BiFe1−xCoxO3 (x = 0.00, 0.03, 0.05, 0.10) nanoceramics, where the average crystallite size and induced strain in these samples are calculated using Scherrer's method and Williamson–Hall equation, respectively. An increasing trend of average crystallite size with increase in dopant concentration was observed. Microstructural examinations of pure and doped BFO identified compact granular shaped microstructures with irregular size and shape but changed to uniform spherical shape after Co substitution up to 10 mol%. Confirmation of the uniform distribution of dopants throughout the sample has been carried out using elemental mapping studies. On the other hand, the chemical states of all the constituent elements were identified by X-ray photoelectron spectroscopic studies. Non-monotonic variations in the real part of dielectric values were observed with increasing Co concentrations. The optical absorption coefficient was found to increase by 35% in 10 mol% Co-doped BFO than that of pure BFO at 480 nm. Optical band gap studies depicted a striking inverse correlation of bandgap values and doping concentration up to 10 mol% Co substitution without varying the intrinsic structural feature of bismuth ferrite. Interestingly, the bandgap value of bismuth ferrite was varied from (2.08 ± 0.02) eV to (1.63 ± 0.02) eV, more in the visible region. The results from present investigations suggest that synthesis techniques and chemical substitution need to be continuously optimized to get desired physical properties suitable for device applications such as photovoltaics.