Improving electromechanical properties in KNANS-BNZ ceramics by the synergy between phase structure modification and grain orientation

Abstract

Faced with an increasingly deteriorating environment, research on environmentally friendly piezoelectric ceramics has become very important. In this work, lead-free 〈00l〉_c-textured and random (1 − x)(K_0.5Na_0.5)_0.98Ag_0.02(Nb_0.96Sb_0.04)O₃ − x(Bi_0.5Na_0.5)ZrO₃ (x = 0.01, 0.02, 0.03, 0.04, 0.05) (abbreviated as T-KNN/x and R-KNN/x, respectively) ceramics with various kinds of phase structures were obtained. Through the combined effect of phase structure modification and grain orientation, a high piezoelectric response (d₃₃ ≈ 550 pC N⁻¹) was realized in T-KNN/0.03 samples with rhombohedral–orthorhombic–tetragonal (R–O–T) phase coexistence, while the optimum piezoelectricity of the random counterparts was obtained in R-KNN/0.04 ceramics possessing the R–T phase boundary. Meanwhile, T-KNN/0.03 and R-KNN/0.04 ceramics exhibited a high Curie temperature (T_C ≈ 250 °C). Moreover, T-KNN/x ceramics showed a different degree of piezoelectricity enhancement compared to their random counterparts. A comparative analysis revealed the underlying mechanism from the perspective of engineering the domain configuration, indicating that a significant enhancement of piezoelectric property in T-KNN/0.03 ceramics should be attributed to the combined effect of R–O–T phase coexistence and favorable engineered domain configuration of the R and O phase. This work demonstrates the vast potential of exploiting phase structure modification and texturing techniques to improve the piezoelectricity of KNN-based piezoceramics.