Effect of Mn4+ doping on the microstructure and electrical property of BiFeO3 ceramic

Multiferroic BiFe1-xMnxO3 (x= 0, 0.05, 0.10, 0.15, 0.20) (represented as BF1-xMxO) ceramics are prepared by the conventional solid state reaction technique. The effects of Mn4+ doping on density, phase structure, morphology, dielectric and ferroelectric properties are investigated. The X-ray diffraction patterns of the samples indicate that the typical perovskite phase structure of BiFeO3 is formed, and a phase transition starts near x= 0.05, i.e., the phase structure is distorted from rhombohedral to orthorhombic by Mn4+ doping. The dielectric susceptibility of the sample is significantly increased and the dielectric loss is slightly increased with the increase of Mn4+ content. The dielectric constant r of the BiFe0.85Mn0.15O3 ceramic at 10 kHz is as high as 1065, 22 times larger than that for pure BiFeO3. It is suggested by hysteresis loop measurements that the ferroelectric property of the BF1-xMxO ceramics is improved and the remanent polarization is increased by Mn4+ doping. This is probably because Mn4+ is more stable than Fe3+, and the B-site doping with higher valent Mn4+ could reduce the volatilization of Bi3+ and suppress the valence fluctuation of Fe3+, thereby reducing the concentration of oxygen vacancies and the leakage current in the ceramic.