Investigations on the structure, defects, electrical and magnetic properties of Ni-substituted BiFeO3 ceramics

Polycrystalline BiFe1-x Ni (x) O-3 (x = 0.00-0.30) ceramics were synthesized by solid state reaction method followed by rapid liquid phase sintering. The effect of Ni substitution on the structure, defects, electrical and magnetic properties of BiFeO3 ceramics was investigated. X-ray diffraction measurements reveal that Ni-substituted samples exhibit distorted rhombohedral perovskite structure as that of unsubstituted BiFeO3, and the impurity phases such as Bi2Fe4O9 decrease due to Ni substitution. The changes in the phonon frequencies in Raman spectra reveal the lattice distortion in Ni-substituted samples which are in agreement with the XRD analysis. Positron annihilation lifetime measurements reveal that cation vacancy-type defects exist in all samples, the vacancy concentration increases with increasing Ni content from 0.00 to 0.30. The enhancement in leakage current and dielectric properties is observed in Ni-substituted samples due to the suppression of impurity phases and Fe2+. Magnetic measurements indicate that the Ni-substituted BiFeO3 samples exhibit weak ferromagnetism. The magnetic properties are found to increase with increasing Ni concentration due to the internal structural distortion, cation vacancy, the ferromagnetic exchange between the neighboring Fe3+ and Ni2+ ions and the change in Fe-O-Fe bond angle.