Ferroelectric Properties of BiFeO_3-M_(0.5)Bi_(4.5)Ti_4O_(15) (M = Na and K) Thin Films Prepared by Chemical Solution Deposition

We explore new systems of BiFeO3-Na0.5Bi4.5Ti4O15 (NaBFT) and BiFeO_3-M_(0.5)Bi_(4.5)Ti_4O_(15) (KBFT) solid solutions, where our interest is focused on ferroelectric properties. The NaBFT and the KBFT thin films were prepared by a chemical solution deposition method. The crystal structure and the surface morphology of the thin films were characterized by means of X-ray diffraction, Raman spectroscopy and scanning electron microscopy. The values of remnant polarization (2P_r) were 76.5 and 70.9 μC/cm^2 at an electric field of 663 kV/cm for the NaBFT and the KBFT thin films, respectively. The values of dielectric constant were 748 and 717 at a frequency of 1 kHz for the NaBFT and the KBFT thin films, respectively. The values of leakage current density of the KBFT and the NaBFT thin films were 6.9 × 10^(-7) and 5.9 × 10^(-6) A/cm^2 at an electric field of 100 kV/cm, respectively. Both thin films showed no polarization fatigue up to 1.4 × 10^(10) switching cycles. The good ferroelectric properties observed in the thin films may be related to the reduction of bismuth vacancies and oxygen vacancies.