Dielectric and piezoelectric properties of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–BiCrO3 lead-free piezoelectric ceramics

A new ternary Bi-based lead-free piezoelectric ceramic system with perovskite structure (1 − x − y)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–yBiCrO3, was prepared by a conventional solid-state reaction method and the effect of amount of Bi0.5K0.5TiO3 and BiCrO3 on microstructure and electrical properties of the ceramics was investigated. The morphotropic phase boundary (MPB) of the system between rhombohedral and tetragonal locates in the range of x = 0.18–0.21, y = 0–0.02. And an obvious second phase was observed in the samples with y = 0.025 and x = 0.24. The addition of BiCrO3 caused an insignificant promoted grain growth and Bi0.5K0.5TiO3 suppressed the growth of grain. The dielectric constant ɛr decreases and dielectric loss tan δ increases with the increase frequency. The optimum piezoelectric properties were obtained near the composition of the MPB. The piezoelectric constant d33 and the electromechanical coupling factor kp show maximum values of d33 = 168 pC/N and kp = 0.32 at x = 0.18, y = 0.015 and x = 0.18, y = 0.01, respectively.