Effect of synthesis conditions on the preparation of BiFeO₃ nanopowders using two different methods

Bismuth orthoferrite (BiFeO₃) nanoparticles have been synthesized via the co-precipitation and the oxalate precursor methods. Effects of Bi source, annealing temperature, Bi/Fe molar ratio, oxalic acid ratio and Mn²⁺ ion on the crystal structure, crystallite size, microstructure and magnetic properties of the produced powders were systematically studied. The results revealed that bismuth oxychloride and iron oxide were formed using chlorides sources. A single phase of BiFeO₃ was formed from as-made samples with Bi/Fe molar ratio 1.1 using nitrate sources and annealed at 500 and 600 °C for 2 h via the two pathways. The pure BiFeO₃ phase appeared as spherical and pseudocubic-like structure using the co-precipitation and the oxalic acid precursor routes, respectively. A high saturation magnetization (3.94 emu/g) was achieved for powder formed from the oxalate precursor route with Bi/Fe molar ratio 1.0 annealed at 600 °C for 2 h as the result of the formation of Bi₂₅FeO₃₉. Moreover, Mn²⁺ ion addition affected BiFeO₃ properties due to the formation of Bi₂Fe₂Mn₂O₁₀. Hence, the saturation magnetization and the coercive force of BiFeO₃ were improved substantially by substitution of Mn²⁺ ions (BiFe_1-XMn_XO₃, X = 0.1–0.2).