Structural analysis of polycrystalline BiFeO₃ films by transmission electron microscopy

A multiferroic polycrystalline BiFeO₃ film has been fabricated by a chemical solution deposition followed by the post deposition annealing at 823 K in air. The nanostructure of the BiFeO₃ film was characterized by transmission electron microscopy (TEM). The nano-beam electron diffraction and the fast Fourier transform pattern image from the high resolution TEM image were compared with the electron diffraction patterns of the multislice simulation, and it was revealed that the BiFeO₃ has R3c rhombohedral structure. Formation of any additional phase or phases was not found in the sample. The BiFeO₃ film shows the small saturation magnetization of 5.2 emu/cm³ without spontaneous magnetization at room temperature, which behavior is typical for the weak ferromagnetic materials. The ferroelectric hysteresis loop of the BiFeO₃ film was measured at low temperature in order to reduce the leakage current. The remanent polarization and the electric coercive field at 90 K were 52 μC/cm² and 0.51 MV/cm at an applied electric field of 1.4 MV/cm, respectively. The structure-magnetic properties relationship is also discussed.