Effect of bivalent Co ion doping on electric properties of Bi0.85Nd0.15FeO3 thin film

The influence of Co2+ ion doping on the structure, fluctuation of Fe valence, leakage current, dielectric, and ferroelectric properties of the Bi0.85Nd0.15FeO3 (BNFO) thin film was investigated. X-ray photoelectron spectroscopy (XPS) confirmed that the concentration of Fe2+ ions in the BNFCO films were lower than that in the BNFO film, and it also evidenced that Co2+ ions doping can restrain the formation of Fe2+ ions and oxygen vacancies. The leakage current density of BNFCOx=0.01 film was reduced by three orders of magnitude compared with the BNFO film. The BNFCOx=0.04 film was subject to a SCLC conduction below 180 kV/cm, while the interface-limited Fowler-Nordheim tunneling dominated its leakage behavior above 180 kV/cm. The strong frequency dependence of the dielectric response implied that dipoles of the charged defects rather than electrons/domains mainly contribute to the characteristics of εr and tan δ of the BNFCO films. A giant remanent polarization of ∼121 μC/cm2 in the BNFCOx=0.03 film was observed, due to the reduced leakage current, improved dielectric constant, and the enhanced anti-breakdown characteristic in the high electric field. In addition, the contribution of dipoles of the charged defects to the ferroelectric behavior of the BNFCO films at low frequency should not be neglected.