The structural, ferroelectric and optical properties of (Gd, Cr) co-substituted BiFeO3 thin films

Polycrystalline BiFeO3 (BFO) and Bi0.9Gd0.1Fe1-xCrxO3 (x=0, 0.025, 0.05, 0.075, 0.10) multiferroic thin films were fabricated on quartz and Pt(111)/Ti/SiO2/Si(100) substrates using a sol-gel method. The effects of (Gd, Cr) co-doping on the microstructural, electrical and optical properties of BFO were studied. X-ray diffraction and micro-Raman measurements demonstrated that the phases of all films were a rhombohedral perovskite structure. The merging of (110) and (104) diffraction peaks demonstrated a structural transition in the Bi0.9Gd0.1Fe1-xCrxO3 thin films. The field emission scanning electron microscopy (FESEM) patterns exhibited that the grain sizes were decreased and the surface textures got denser and glossier with the increasing Cr content. The Bi0.9Gd0.1Fe0.95Cr0.05O3 showed a more uniform grain size distribution and denser surface. The leakage current densities and electrical polarizations of (Gd, Cr) co-doped BFO were improved. A minimum leakage current density (5.32x10(-9)A/cm(2)) was obtained in Bi0.9Gd0.1Fe0.95Cr0.05O3 thin films at the electric field of 300kV/cm, which decreased by four and five orders of magnitude compared to the BGFO thin film (4.17x10(-5)A/cm(2)) and BFO thin film (6.5x10(-4)A/cm(2)), respectively. And larger polarizations were observed in Bi0.9Gd0.1Fe0.95Cr0.05O3 thin film. Moreover, the leakage current mechanisms of all films have been studied. The optical band gaps (E-g) of Bi0.9Gd0.1Fe1-xCrxO3 thin films were blue-shift with the increasing of x value, which suggested a promising applications in the field of photocatalysis and power electronic devices.