Study of structural, optical and enhanced multiferroic properties of Ni doped BFO thin films synthesized by sol-gel method

Pure and nickel (Ni) doped bismuth ferrite (BiFeO3, BFO) thin films were successfully deposited on the SnO2:F (FTO)/glass substrate by a sol-gel method. The structure, phase evolution, chemical composition, surface element chemical states, surface morphology, multiferroic and optical properties were systematically investigated. The structural analyses using XRD and Raman techniques revealed that Ni doping induced a structure transition from rhombohedral toward orthorhombic or tetragonal structure. The surface element chemical states examined by XPS demostrated that Ni doping resulted in the increase of oxygen vacancies while decrease of Fe2+ concentration. SEM images demonstrated that Ni doping impacted the grain growth mechanism and the average grain size increased with increase of Ni doping. EDS analysis further confirmed the element composition with presence of Ni element in the Ni doped BFO thin films. The leakage current density of Ni doped BFO thin films was observed to increase with increase of Ni doping due to the higher oxygen vacancies. An enhanced ferroelectric and piezoelectric properties were obtained in the BFO thin film with Ni doping x = 0.10, giving a high remnant polarization (2Pr) of 22.95 μc/cm2 with a coercive field (2Ec) of 728.24 kV/cm and high piezoelectric coefficient (d33,eff) of 37.76 p.m./V. Meanwhile, the magnetization measurement revealed that Ni doped BFO thin films showed an enhanced magnetization, compared to pure BFO thin film. The highest saturation of 2.85 emu/cm3 under a magnetic field of 10 k Oe is also observed in BFO thin film with Ni doping x = 0.10. The transmittance and optical band gap decreased with increase of Ni doping and when Ni doping is x = 0.10, the lowest band gap of 2.46 eV was observed. © 2020 Elsevier B.V.