Preparation And Characteristic Research On Doped BiFeO₃ Ceramics

Ferroelectromagnets are a kind of multiferroic materials which have both ferroelectric order and ferromagnetic order at certain temperature. Ferroelectromagnets have great potential in the field of information storage, spin electronics, non-linear magnet-light effect, transducer and driver system with their coupling of ferroelectric order and ferromagnetic order. BiFeO3 is one kind of few single-phase ferroelectromagnetic materials which simultaneously possesses ferroelectric and anti-ferromagnetic order at room temperature. However BiFeO3 has also disadvantages of large leakage current, low magnetization and small magnetoelectronic coupling effect.In this paper, La3+, Nd3+ and Mn3+ doped BiFeO3 ceramics were prepared by soft chemical method with tartaric acid used as chelant. Phase purity and microstructure of the ceramics were characterized by X-ray diffraction meter and scanning electronic microscope, respectively. The ferroelectric and dielectric properties of the ceramics were also investigated.The experiment showed that, BiFeO3 powders of pure phase were obtained after being calcined at 500℃. However, there was remnant carbon. After being calcined at 700℃, remnant carbon had been all eliminated.Doping is easier to obtain pure BiFeO3 phase. There existed impure phase in non-doped BiFeO3 ceramic in the sintering temperature range of 800℃to 950℃. While in the doped BiFeO3 ceramics, with the increasing of doping content, the sintering temperature that made impure phase disappear became gradually lowered. The microstructure was denser, the grains were smaller, and the cell parameter became smaller; The grains of La,Nd-doped ceramics grew rapidly at 950℃. When at the same doping content and sintering temperature, the grain size of Nd-doped ceramics was smaller than that of La-doped ceramics; With the increasing of sintering time, the phase purity didn't change evidently, the grains were larger and the microstructure was denser. And when sintered at 900℃for 10h, the grain shape of Mn-doped BiFeO3 ceramic suddenly changed into tetragon;All doped ceramics were examined on their electronic characteristics. The results indicated that their dielectric tangents were relatively smaller than those reported in other articles. Doping had in some way suppressed leakage current, lowering dielectric tangent. But saturated ferroelectric hysteresis loops weren't saturated at room temperature, which suggested the electric characteristics of the doped ceramics was still needed to be improved.