Comparative studies of pure, Ca-doped, Co-doped and co-doped BiFeO3 nanoparticles

BiFeO3 and Ca, Co doped BiFeO3 nanoparticles have been synthesized by the sol–gel method. Rietveld refinement of X-ray diffraction data and Raman spectra reflect a structural phase transition from rhombohedral (pure BiFeO3) to two phase coexistence (rhombohedral R3c and cubic PM-4M) in case of Bi0.9Ca0.1FeO3 and Bi0.9Ca0.1Fe0.95Co0.05O3, which indicate that Ca doping can induce the obvious change of crystal structure while Co doping cannot. An apparent blue-shift can be observed in all the doped samples along with a decrease of the direct optical band gap compared with pure BiFeO3. XPS results reveal that Ca and Co doping increases the Fe3+ ions (unidoped samples show better results), which could be an evidence for decrease of oxygen vacancies and enhancement of magnetism. Ca and Co uni-doped into BiFeO3 can enhance magnetism due to different mechanisms, more interestingly, the room temperature magnetic hysteresis (M–H) curve shows the largest saturation magnetization value in Ca, Co co-doped samples.