Crystal Structure and Spontaneous Magnetism of BiFeO_3 Powder Synthesized by Hydrothermal Method

摘要

Single-phase BiFeO_3 powder was successively synthesized by a low-temperature hydrothermal method. Scanning electron microscopy and transmission electron microscopy results showed that BiFeO_3 powder had several hundred nanometers to micrometer-sized particles with a broad size distribution. BiFeO_3 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 A 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 FeO_6 octahedras. The weak ferromagnetism observed in the hydrothermal BFO powder is ascribed to the displacive disorder of FeO_6 octahedras resulting in an incomplete counterbalance between the antiferromagnetic sublattices of the Fe-ions.