Crystal Structure and Spontaneous Magnetism of BiFeO₃ Powder Synthesized by Hydrothermal Method

Single-phase BiFeO₃ powder was successively synthesized by a low-temperature hydrothermal method. Scanning electron microscopy and transmission electron microscopy results showed that BiFeO₃ powder had several hundred nanometers to micrometer-sized particles with a broad size distribution. BiFeO₃ powder showed weak-ferromagnetic behavior with a small magnetization value (M _S ∼ 20 memu/g) at room temperature. Rietveld refinement results for the crystal structure show the displacive disorder of the Fe-site(6a); the Fe-site(6a) splits into two pairs, Fe(1) and Fe(2) displaced by 0.9 Å from each other and these sites are partially occupied. Hence the O-site(18b) also splits into the two partially occupied sites forming a distorted FeO₆ octahedras. The weak ferromagnetism observed in the hydrothermal BFO powder is ascribed to the displacive disorder of FeO₆ octahedras resulting in an incomplete counterbalance between the antiferromagnetic sublattices of the Fe-ions.