Effects of Heat-Treatment Temperature on the Properties of (1-x)(Na_0.5Bi_0.5)TiO₃-xBiAlO₃ Lead-Free Piezoelectric Thin Films

Lead-free sodium bismuth titanate-aluminate bismuth [0.97(Na_0.5Bi_0.5)TiO₃-0.03BiAlO₃] solid-solution films deposited on (100) Pt/TiO₂/SiO₂/Si substrates by a sol-gel process were pyrolyzed and annealed at different temperatures. The film annealed at 725°C with a pyrolysis temperature of 410°C exhibited the optimal electrical properties and excellent piezoelectric properties, with a remanent polarization 2P_r of 38 μC/cm² and a leakage current density of 10^-7-10^-6 A/cm² (E < 200 kV/cm). The values of the dielectric constant and dissipation factor at 100 kHz were 422 and 0.039, respectively. The piezoelectric coefficient of the film after poling at 168 kV/cm was found to be 57 pm/V, making the BNT-BA films a viable lead-free alternative to the lead-based materials in such as biosensors and ultrasonic transducers.