Piezoelectric K0.5 Na0.5 NbO3 thick films derived from polyvinylpyrrolidone-modified chemical solution deposition

Lead-free K0.5 Na0.5 NbO3 (KNN) ferroelectric films with enhanced thickness of 3.5 μm were prepared by a polyvinylpyrrolidone-modified chemical solution deposition method. A single perovskite phase with a dense morphology and (100) orientation was obtained at relatively low annealing temperature of 600 °C. A large effective piezoelectric coefficient d33, of 61 pm/V was demonstrated at 100 kHz without considering the substrate clamping effect. A well-saturated polarization hysteresis loop was obtained with a high remnant polarization Pr of 16.4 μC/ cm2. These results showed that KNN is a promising lead-free piezoelectric film candidate, and that crystallizing the film at low processing temperature to obtain (100) orientation and dense morphology is critical to achieving excellent ferroelectric and piezoelectric properties.