The structural, optical, ferroelectric properties of (1-x)BiFeO3-xCaTiO3 thin films by a sol–gel method

Abstract

(1-x)BiFeO3-xCaTiO3 ((1-x)BFO-xCTO, x = 0, 0.05, 0.10, 0.15, 0.20) thin films were successfully grown on Pt(111)/Ti/SiO2/Si(100) substrates using a sol–gel spin coating method. The structure stabilities of BFO thin films were improved by introducing CTO due to the increase of their tolerance factor. The X-ray diffraction patterns indicated that all the samples had a single perovskite structure. The merging phenomenon of (110) and (104) diffraction peaks demonstrated a distortion of the lattice structure in BFO thin films by introducing CTO. The atomic force microscope showed all the samples had dense, crack-free and uniform morphology. The leakage current density decreased with the increasing of CTO contents. At the applied electric field of 300 kV/cm, the leakage current density of the 0.85BFO-0.15CTO was 1.42 × 10−8 A/cm2, which is about 4 orders of magnitude lower than that of the pure BFO thin film (5.78 × 10−4 A/cm2). The leakage conduction mechanism showed Ohmic conduction for all thin films in the low electric field region. In the high electric field region, the leakage mechanisms were dominated by the space-charge-limited current behavior for 0.80BFO-0.20CTO and the Fowler-Norheim tunneling for (1-x)BFO-xCTO (x = 0.10, 0.15) thin films. The remnant polarization (2P r ) and spontaneous polarization (P s ) of (1-x)BFO-xCTO (x = 0.10, 0.15, 0.20) were obviously improved. The 0.85BFO-0.15CTO thin film showed the best ferroelectricity with large remnant polarization of 39.88 μC/cm2 while the remnant polarization of the pure BFO was 3.74 μC/cm2 at the electric field of 300 kV/cm. The absorption edges of (1-x)BFO-xCTO thin films are blue-shift with the increasing of x value. The structural, optical properties and ferroelectricity of BFO thin films were improved by introducing CTO.