Lead-free piezoelectric KNN-BZ-BNT films with a vertical morphotropic phase boundary

The lead-free piezoelectric 0.915K_0.5Na_0.5NbO₃-0.075BaZrO₃-0.01Bi_0.5Na_0.5TiO₃ (0.915KNN-0.075BZ-0.01BNT) films were prepared by a chemical solution deposition method. The films possess a pure rhomobohedral perovskite phase and a dense surface without crack. The temperature-dependent dielectric properties of the specimens manifest that only phase transition from ferroelectric to paraelectric phase occurred and the Curie temperature is 217 ^oC. The temperature stability of ferroelectric phase was also supported by the stable piezoelectric properties of the films. These results suggest that the slope of the morphotropic phase boundary (MPB) for the solid solution formed with the KNN and BZ in the films should be vertical. The voltage-induced polarization switching, and a distinct piezo-response suggested that the 0.915 KNN-0.075BZ-0.01BNT films show good piezoelectric properties.