Comparative study on substitution effects in BiFeO3 thin films fabricated on FTO substrates by chemical solution deposition

Pure BiFeO3 (BFO), BiFe0.97Co0.03O3−δ (BFCO) and Bi0.90Gd0.10Fe0.97Co0.03O3−δ (BGFCO) thin films were successfully deposited on FTO substrates by chemical solution deposition technique. The field emission scanning electron microscope reveals that the surface morphology of the BGFCO thin film becomes more compact and uniform than that of the other two films. A slight lattice distortion is created in the BFCO thin film, whereas 10% Gd doping gives rise to tetragonal phase transition and (1 1 0) preferentially oriented film texture for the BGFCO thin film, as evidenced by Raman scattering spectra and X-ray diffraction analyses. X-ray photoelectron spectroscopy analyses clarify that Co-doping results in the increase of oxygen vacancy concentration in the BFCO film, while further introduction of Gd into the BFCO lattice can decrease oxygen vacancy concentration, and the concentrations of Fe2+ ions in the BFCO and BGFCO thin films are less than that in the BFO counterpart. The BFCO film shows the improved remanent polarization (Pr) of 11.2 μC/cm2 compared with that of 1.4 μC/cm2 for the BFO film. The high breakdown strength, low leakage current density in the high electric filed, improved dielectric properties as well as the increased stereochemical activity of Bi ion lone electron pair of the BGFCO thin film all together contribute to the giant Pr of 139.6 μC/cm2 at room temperature.