New lead-free piezoelectric thin film fabricated using metal-oxide nanosheets at low temperature

A new lead-free piezoelectric film consisting of Sr₂NaNb₄O₁₃ ⁻ (SNNO⁻) and TiNbO₅ ⁻ (TNO⁻) nanosheets was fabricated via electrophoresis. SNNO and TNO films display paraelectric polarization versus electric field (P-E) loops. However, a new film composed of a mix of SNNO⁻ and TNO⁻ (S/T) nanosheets displayed a ferroelectric P-E hysteresis loop with large maximum polarization (18.7 μC/cm²), remnant polarization (7.7 μC/cm²), and a coercive electric field (86 kV/cm). The interfaces formed between the SNNO and TNO layers induced ferroelectric properties in the S/T film through the occurrence of polar distortion and octahedral tilting in the film. Ferroelectric properties were also observed in piezoelectric force microscopy images of the S/T film, which showed 90° domains after the removal of the applied electric field. The dielectric constant of the S/T film was 70, which is higher than those of SNNO and TNO films, indicating that the S/T film is a ferroelectric material. The piezoelectric strain constant of the S/T film was 156 p.m./V and promising insulating properties were observed therein. The growth temperature of the S/T film was low (300 °C), suggesting that the S/T film can be used for flexible electronic devices.