Mechanism of improving ferroelectric properties of BiFe0.98M0.02O3 (M = Zn, Al, Ti) polycrystalline films.

Pure BiFeO₃ (BFO) and (Zn²⁺, Al³⁺, Ti⁴⁺) mono-doped BiFe_0.98M_0.02O₃ (M = Zn, Al, Ti) polycrystalline multiferroic films has been successfully synthesized on FTO/glass substrates via sol–gel spin-coating method. Effects of mono-doping with three different valence metal ions (Zn²⁺, Al³⁺, Ti⁴⁺) on crystalline structure, surface morphology, and electrical properties of BFO films were systematically investigated. X-ray diffraction (XRD) results show that BFO film samples mono-doped with Zn²⁺, Al³⁺, and Ti⁴⁺ all have rhombic distorted perovskite structure of R3m space group, and no heterophases are produced. Scanning electron microscope (SEM) images reveal that microstructural density of BiFe_0.98M_0.02O₃ (M = Zn, Al, Ti) films is significantly increased compared to pure BFO. Furthermore leakage current densities of BiFe_0.98M_0.02O₃ (M = Zn, Al, Ti) films all reach up to the order of 10⁻⁵ A/cm² under applied electric field of 150 kV/cm, that is about three orders of magnitude lower than pure BFO films. Greatly reduced leakage current density confers superior ferroelectric properties to BiFe_0.98M_0.02O₃ (M = Zn, Al, Ti) films, as evidenced by beautiful P–E hysteresis loops at room temperature for (Zn²⁺, Al³⁺, Ti⁴⁺) mono-doped BiFe_0.98M_0.02O₃ (M = Zn, Al, Ti) films and significantly higher double remnant polarization (2P_r ~ 164.75–168.66 μC/cm²) values compared to pure BFO (102.36 μC/cm²). The significantly improved ferroelectric properties provide a new reference for the practical application of BFO film. [ABSTRACT FROM AUTHOR]