Effects of BaTiO₃ Content and Mn Doping on Ferroelectric Properties of NaNbO₃–BaTiO₃ Thin Films Prepared by Chemical Solution Deposition

Lead-free ferroelectric NaNbO₃–BaTiO₃ thin films were prepared by chemical solution deposition. Perovskite single-phase NaNbO₃–BaTiO₃ thin films were successfully fabricated at 550 °C on Pt/TiO_x/SiO₂/Si substrates. The ferroelectric properties of the NaNbO₃–BaTiO₃ thin films depended on the BaTiO₃ content of NaNbO₃–BaTiO₃. Among NaNbO₃–BaTiO₃ films with various BaTiO₃ concentrations, the 0.95NaNbO₃–0.05BaTiO₃ thin films showed relatively large polarization at -190 °C, although the insulating resistance of the films was not sufficiently high at room temperature. To improve the electrical resistivity at ambient temperatures, Mn doping of 0.95NaNbO₃–0.05BaTiO₃ was examined. The leakage current density of the films was found to be greatly reduced by a small amount of Mn doping. 1.0 mol % Mn-doped 0.95NaNbO₃–0.05BaTiO₃ thin films showed well-shaped slim ferroelectric polarization–electric field (P–E) hysteresis loops at room temperature. The remanent polarization (P_r) and coercive field (E_c) values of the 1.0 mol % Mn-doped 0.95NaNbO₃–0.05BaTiO₃ thin films at 1 kHz were approximately 5 µC/cm² and 50 kV/cm, respectively. Furthermore, the ferroelectric P–E loops of the 1.0 mol % Mn-doped 0.95NaNbO₃–0.05BaTiO₃ thin films showed good frequency dependence and could be characterized at a frequency as low as 1 Hz.