Enhanced ferroelectric properties of (Zn, Ti) equivalent co-doped BiFeO3 films prepared via the sol-gel method

High-quality BiFe1-2xZnxTixO3 (BFZTO with x = 0, 0.01, 0.02, 0.03, 0.04, and 0.05) films were successfully prepared on fluorine-doped tin oxide (FTO)/glass substrates via the sol-gel method. The influence of (Zn, Ti) equivalent co-doping on the structure, surface morphology, and ferroelectric properties of BFZTO films was investigated systematically. X-ray diffraction (XRD) and Raman spectra analysis indicate that co-doping results in structural transformations. Scanning electron microscope (SEM) images show that BFZTO films with x = 0.02 exhibit uniform fine grains and higher density, which is instrumental for the development of ferroelectric properties. X-ray photoelectron spectroscopy (XPS) analysis reveals that BiFe0.96Zn0.02Ti0.02O3 film can inhibit the conversion of Fe3+ into Fe2+, thereby greatly reducing oxygen vacancy concentration. Therefore, under the electric field strength of 150 kV/cm, BiFe0.96Zn0.02Ti0.02O3 film was found to have the lowest leakage current density, J = 1.13 x 10-6 A/cm2, which is five orders of magnitude lower than that of pure BiFeO3 (BFO) film. Furthermore, this film exhibits the largest remnant polarization at room temperature, Pr = 131.9 mu C/cm2, which is more than twice as large as that of pure BFO (Pr = 52.6 mu C/cm2). Additionally, by comparing P-E hysteresis loops of different regions on the surface of BiFe0.96Zn0.02Ti0.02O3 film, it was found that the film has high uniformity and stable overall performance. Dielectric and magnetic properties were also enhanced via (Zn, Ti) codoping.