Phase coexistence induced strong piezoelectricity in K0.5Na0.5NbO3-based lead-free ceramics

Abstract

For perovskite ceramics, the ferroelectric phase boundary plays an important role in improving the piezoelectricity of the materials. In this work, (1 − x)(K_0.5Na_0.5)NbO₃ − x[NaSbO₃ + Bi_0.5(Na_0.8K_0.2)_0.5(Zr_0.5Hf_0.5)O₃] lead-free ceramics with R-O-T ferroelectric phase coexistence were developed and the relationship between the phase structure and piezoelectricity was investigated in detail. As x increases, the transition temperature of the rhombohedral and orthorhombic phases (T_R-O) increases, while the orthorhombic–tetragonal phase transition temperature (T_O-T) decreases. When 0.04 ≤ x ≤ 0.05, three ferroelectric phases (R-O-T) coexist near room temperature in the ceramics. Due to the highly consistent orientation of the ferroelectric dipole and the free energy flattening and a low energy barrier induced by the coexistence of three ferroelectric phases (R-O-T), excellent piezoelectric performances of d₃₃ = 452 pC N⁻¹, k_p = 63% and ε_r = 4414 are achieved at x = 0.04. Our study suggests that compared with two ferroelectric phase boundaries (R-O and O-T), the coexistence of the three ferroelectric phases (R-O-T) can effectively enhance the piezoelectric properties of (K_0.5Na_0.5)NbO₃-based ceramics.