Effects of annealing temperature on the structures, ferroelectric and magnetic properties of Aurivillius Bi ₅Ti ₃FeO ₁₅ polycrystalline films

The effects of annealing temperature on the structures, ferroelectric and magnetic properties of Aurivillius layer-structured Bi ₅Ti ₃FeO ₁₅ (BTF) films were investigated. It was found that an annealing temperature above 625 °C can lead to the appearance of Bi ₄Ti ₃O ₁₂ (BiT) secondary phase on Pt substrates. The reduction of the grain sizes was simultaneously confirmed by X-ray diffraction and atomic force microscopy with the introduction of the BiT phase. Moreover, the remanent polarization and coercive field of the BTF films were dramatically enhanced with the introduction of the BiT phase. Improved ferromagnetism for the BTF films was demonstrated upon increasing annealing temperature. Our data indicated that the ferroelectricity strongly correlated with the growth orientation of the BTF films. Finally, the possible factors for the obvious increase of the remanent polarization and coercive field, and the possible reasons for the enhanced ferromagnetic properties were discussed with increasing annealing temperature.