Synergistic effects of Ca 2+ and high-valence Nb 5+ co-doping on the structural, optical and magnetic properties of BiFeO 3

The structural, optical and magnetic properties of BiFeO3, BiFe0.99Nb0.01O3 and Bi1−xCaxFe0.99Nb0.01O3 (BCFNO, 0 ≤ x ≤ 0.25) nanoparticles synthesized via sol–gel method are investigated. It has been found that a phase transition from the rhombohedral R3c structure (x ≤ 0.10) to the ideal cubic perovskite structure (x = 0.25) which can be attributed to Ca2+ doping. Increasing Ca2+ dopants results in the increase of oxygen vacancies. As doping amount x increase, the bandgap of BCFNO decreases and the valence band spectra indicates that it’s a p-type semiconductor, which indicates their favorable potential in photocatalytic applications. The remnant magnetization Mr of BCFNO reaches a maximum value (0.146 emu/g about 15 times compared with pure BFO) at x = 0.10. This enhancement of magnetic properties in BCFNO can be ascribed to the synergistic effect of A and B site ions co-doping. Higher valance Nb doping cause the size effect and the magnetic polarons bounded to the impurities by Ca ions.