Effect of annealing atmosphere on the structural and electrical properties of BiFeO3 multiferroic ceramics prepared by sol–gel and spark plasma sintering techniques

Phase-pure BiFeO 3 powders were synthesized by sol–gel technique. Based on these powders, high-density BiFeO 3 ceramics were prepared by spark plasma sintering (SPS) at 700   °C along with annealing for 2 and 4   h, respectively, at 650   °C under atmospheres of air and oxygen. X-ray diffraction analysis revealed that the 4   h-oxygen-annealed sample contained a single rhombohedral perovskite phase while the samples annealed in the other conditions contained small quantities of impurity phases besides the rhombohedral perovskite phase. The relative density of the 4   h-oxygen-annealed sample was about 96%, being apparently higher than that of the other samples. In comparison with the 4   h-air-annealed sample, the dielectric constant of the 4   h-oxygen-annealed sample was relatively higher. The activation energy for electrical conduction was about 1.17   eV for the 4   h-oxygen-annealed sample while it was about 0.98   eV for the 4   h-air-annealed sample, showing that the former would have a lower room-temperature conductivity (~2.6×10 −14   S   cm −1 ) than the latter (~2.1×10 −13   S   cm −1 ). It is therefore anticipated that the oxygen-annealed sample could possess better ferroelectric properties as compared to the air-annealed sample.